Legends of Runeterra's Content Design Lead has confirmed on Twitter that the Celestial cards you'll see are not completely random.
- Units will be seen more than Spells.
- High-cost cards are less frequently seen.
Oof. Someone gave you outdated information. Celestials have an individual weighting, but it's not so extreme. Generally, units are a little more frequent than spells and high cost cards are a little less frequent. At the extreme, some celestials are 2x as likely as some others.