I have 3 nerf suggestions to nerf warlock quest:

1) make some cards banned to use with the questline.. for example crystalizer, spirit bomb, stealer of souls.. (pick up your choice)

2) change Tamsin's Battlecry to: for the rest of the game, whenever your hero takes damage on your turn enemy hero takes it as well.. this is better than reverting all the damage your hero takes to the enemy hero because that sounds stupid and unfair

A sidenote:
Tamsin's Battlecry voice line says: "all of stormwind shall *SHARE* my pain" and this nerf suggestion above is the actual meaning of "share"

3) you could also make the questline progress harder by changing if from taking points of damage on your turn.. to how many times you took damage on your turn.. which means the questline should say: "take damage X times on your turn" instead of: "take X points of damage on your turn"

And the last nerf suggestion will be great to slow down the questline unless blizzard some day prints a card that can deal sperated damage to your hero.. in that case you could just change the questline progress mechanic to: "play X cards that deal damage to your hero"

Sorry my English is not perfect, feel free to tell me your thoughts, and hopefully i didn't miss or mess up something, thanks for your time :)