OP's proposal may not be the best, and will most likely not be the result that Blizzard goes with, but the premise and the understanding that something is fundamentally broken with Warlock is accurate and well founded. You seemed to miss that point and focus entirely on the details and not the whole picture…
I don't believe I've missed anything. I never disputed that Warlock has been overtuned/warping the meta since United in Stormwind launched. The OP said "I'd love to hear feedback about this [proposed nerf]," so I offered some feedback on the details of their proposed nerfs.
Quote From Sykomyke
In that sense, your proposal looks a lot like a convoluted way to remove the lifesteal from the quest
It's not, but even assuming that was the case: in standard that isn't so bad. I've literally seen warlocks heal for more damage than they've dealt to themselves through the use of soul fragments, Soul Shear, Drain Soul, Blood Shard Bristleback, and Touch of the Nathrezim. Coupled with Tamsin (legendary) they can duplicate many of those spells because they are all CHEAP spells that are easy to copy with Tamsin for 0 cost, free healing.
My point here is that both the proposed change and the much simpler "remove lifesteal" idea I've seen bounced around results in an approximately 50% increase to the amount of net damage you'd need to take to complete the questline. That's enormous. This proposal also makes it a much slower process by removing Life Tap as a source of quest progress, meaning some of the healing that currently keeps Warlock in the game (i.e. the quest rewards) would be delayed. I really don't think you can overstate how dramatically that would weaken every version of this deck against aggro, regardless of whether or not the deck has free mid to late game healing combos with Tasmin and various Shadow spells.
Quote From Sykomyke
It's not some boogie man "ooh, I hate fatigue games, they are so boring and take forever", it's there to END drawn out games. And despite your protests of 'caring too much' it's not something that should be avoidable permanently. (Cards like mal'ganis which allow you to be immune to damage but the vulnerability of taking out malganis still exists are ok). But a permanent battlecry is not cool.
And even Kibler himself agreed that it ignoring fatigue feels like an odd design decision. (not that I'm citing Kibler as some gospel, but as someone who worked on the physical WoW card game…effectively the precursor to Hearthstone, I feel like his opinion usually isn't far from the truth)
I don't think fatigue is being treated as a boogey man, and I'm not saying its definitely better to include it as part of the effect, but I also don't think it's super relevant here. For starters, redirecting your fatigue damage doesn't negate its central purpose as a way to end drawn out games. Those games will still end in fatigue - they'll just do so in a lopsided way. More to the point, though, these questline decks aren't trying to win by going to fatigue - they're trying to win by hitting you in the face with giants. Yes, they can burn their own deck to get to fatigue quickly, but that's secondary to what they're actually trying to accomplish, and would make for a very weak way to win the game against aggro or midrange strategies if it were all they had going for them.
I agree that Kibler usually has a lot of good takes on these things, and one of the points he made in his Combos video on YouTube was that the biggest problem with decks like this (i.e. decks that are not necessarily OP but still warp the meta) is their popularity. At the time he made the video, these kinds of unbeatable combo decks were something like 30% of the meta, which is too high for control decks to have a lot of success (i.e. any control deck in a meta like that would need to have winrates against aggro that are well above 70%, which is a very tall order).
Nuking this quest is a great way to dramatically decrease that number, but there are better ways to tackle the actual combo pieces that are causing the problems, which in turn will weaken the quest in its weaker matchups and ultimately make it less popular. To their credit, Blizzard has already been nerfing these pieces. I know that mostly only helps Standard players, but the fact is the Wild format is too highly synergistic to do much about this quest without banning it or radically changing a lot of old cards (which Blizzard hates to do in Wild).
This proposal seems pretty bad to me, and basically a nuke from orbit for most versions of the deck. A typical self-harm Warlock card deals two to three damage to your hero. So you'd go from 6/7/8 damage to something close to 7/10/12 (i.e. a change from a net 15 damage to 23 damage). In that sense, your proposal looks a lot like a convoluted way to remove the lifesteal from the quest, which I believe would make the quest totally unplayable (particularly after rotation) due to how weak it would be to aggro after sustaining that much damage.
But it's actually even worse than that. If you assume that average self-harm value is three (which is reasonable considering the popularity of cards like Raise Dead, Flame Imp, Backfire, and Hecklefang Hyena in many Questline Warlock decks), the quest would end up dealing 36 damage to your hero in order to restore six health and get Blightborn Tamsin. You'd literally have to kill your own hero to complete the quest.
One of the interesting things about the current design of damage dealt rather than instances of damage dealt is that there are times when you waste damage (e.g. you're at 5/6 for the first quest reward and you tap, wasting one point of damage). I think that's a positive aspect of the quest today because, for decks that care about quest completion, it forces you to think pretty critically about how to spend your damage to avoid getting demolished by aggro.
I also think you care too much about fatigue. You describe it as a lose condition, but it's very rare that any game actually goes to fatigue, so it's also mostly irrelevant as a way to lose. Fatigue is a major part of certain Questline archetypes (like the Stealer version of the deck that used it for burst), but latest nerf that moved Stealer of Souls up to 6 mana has really weakened that version of the deck, and it's mostly gone from the Standard meta.
One last note, I don't know that this proposal would do anything to impact the most popular version of Questline Warlock - the Handlock/Flesh Giant version. That version doesn't really try to complete the quest anyway, and Life Tap would still reduce the cost of the giants even if it doesn't proc the quest. That version is also probably the only one still viable in Standard after the latest nerfs, making your proposal all the more moot.
I don't believe I've missed anything. I never disputed that Warlock has been overtuned/warping the meta since United in Stormwind launched. The OP said "I'd love to hear feedback about this [proposed nerf]," so I offered some feedback on the details of their proposed nerfs.
My point here is that both the proposed change and the much simpler "remove lifesteal" idea I've seen bounced around results in an approximately 50% increase to the amount of net damage you'd need to take to complete the questline. That's enormous. This proposal also makes it a much slower process by removing Life Tap as a source of quest progress, meaning some of the healing that currently keeps Warlock in the game (i.e. the quest rewards) would be delayed. I really don't think you can overstate how dramatically that would weaken every version of this deck against aggro, regardless of whether or not the deck has free mid to late game healing combos with Tasmin and various Shadow spells.
I don't think fatigue is being treated as a boogey man, and I'm not saying its definitely better to include it as part of the effect, but I also don't think it's super relevant here. For starters, redirecting your fatigue damage doesn't negate its central purpose as a way to end drawn out games. Those games will still end in fatigue - they'll just do so in a lopsided way. More to the point, though, these questline decks aren't trying to win by going to fatigue - they're trying to win by hitting you in the face with giants. Yes, they can burn their own deck to get to fatigue quickly, but that's secondary to what they're actually trying to accomplish, and would make for a very weak way to win the game against aggro or midrange strategies if it were all they had going for them.
I agree that Kibler usually has a lot of good takes on these things, and one of the points he made in his Combos video on YouTube was that the biggest problem with decks like this (i.e. decks that are not necessarily OP but still warp the meta) is their popularity. At the time he made the video, these kinds of unbeatable combo decks were something like 30% of the meta, which is too high for control decks to have a lot of success (i.e. any control deck in a meta like that would need to have winrates against aggro that are well above 70%, which is a very tall order).
Nuking this quest is a great way to dramatically decrease that number, but there are better ways to tackle the actual combo pieces that are causing the problems, which in turn will weaken the quest in its weaker matchups and ultimately make it less popular. To their credit, Blizzard has already been nerfing these pieces. I know that mostly only helps Standard players, but the fact is the Wild format is too highly synergistic to do much about this quest without banning it or radically changing a lot of old cards (which Blizzard hates to do in Wild).
This proposal seems pretty bad to me, and basically a nuke from orbit for most versions of the deck. A typical self-harm Warlock card deals two to three damage to your hero. So you'd go from 6/7/8 damage to something close to 7/10/12 (i.e. a change from a net 15 damage to 23 damage). In that sense, your proposal looks a lot like a convoluted way to remove the lifesteal from the quest, which I believe would make the quest totally unplayable (particularly after rotation) due to how weak it would be to aggro after sustaining that much damage.
But it's actually even worse than that. If you assume that average self-harm value is three (which is reasonable considering the popularity of cards like Raise Dead, Flame Imp, Backfire, and Hecklefang Hyena in many Questline Warlock decks), the quest would end up dealing 36 damage to your hero in order to restore six health and get Blightborn Tamsin. You'd literally have to kill your own hero to complete the quest.
One of the interesting things about the current design of damage dealt rather than instances of damage dealt is that there are times when you waste damage (e.g. you're at 5/6 for the first quest reward and you tap, wasting one point of damage). I think that's a positive aspect of the quest today because, for decks that care about quest completion, it forces you to think pretty critically about how to spend your damage to avoid getting demolished by aggro.
I also think you care too much about fatigue. You describe it as a lose condition, but it's very rare that any game actually goes to fatigue, so it's also mostly irrelevant as a way to lose. Fatigue is a major part of certain Questline archetypes (like the Stealer version of the deck that used it for burst), but latest nerf that moved Stealer of Souls up to 6 mana has really weakened that version of the deck, and it's mostly gone from the Standard meta.
One last note, I don't know that this proposal would do anything to impact the most popular version of Questline Warlock - the Handlock/Flesh Giant version. That version doesn't really try to complete the quest anyway, and Life Tap would still reduce the cost of the giants even if it doesn't proc the quest. That version is also probably the only one still viable in Standard after the latest nerfs, making your proposal all the more moot.