I’m reasonably sure you are right on this.
Part of me wants to think that in 2.4, all one needed was one copy of a spell to drop and then it could be evolved to extent that a player had resources to do so, all the way to Mythic. So, the rarer drop rates were acceptable there.
In 2.5, however, players need many copies of the same spell to drop for a single ascension. At the higher rarities, multiple hundreds of copies of the same spell are needed (no one should be expecting to farm Epic/Legendary spell [page] drops). The current drop rates are too low, even when focusing on farming a specific spell’s dungeon.
I would fairly confidently argue that it is perhaps harder to upgrade/evolve spells currently in the new system. Drop rates do not need to be walk-in-the-park / raining-like-candy easy to farm, but they could use some kind of boost. I’m sure the Team is collecting data on drop rates for evaluation. Hardcore players are likely to slowly but surely power through the slog, but I have to wonder how difficult it is for the newer player experience, even with the significantly lower page quantity hurdles to overcome for the lower spell rarities.