I think the main reason the game is easy, is because Devils don't have a lot of health. If you're soul level 35+, most Devils go down in a few hits. That means at best you might get assaulted by their mechanics once. Hell you may not even see all of their mechanics, because of how quickly you can put them down. And this isn't with buffs and magic. Your standard attack hits like a goddamn truck. I remember Shadow Girl, Cait Sith, and Lizard Girl all went down in 3 hits. School Girl went down in I think 4. In fact out of all 7 Devils in Part 1, Siren was the only long fight with interesting mechanics that forced you to heal up.
It got me thinking how much of a difference would it make as far as difficulty is concerned, if their HP got significant buffs. Because if they survive long enough, that's more time for them to apply their debuffs on you, get your Libido bar up, whittle your faith down, etc. If your standard attacks at a decent soul level are enough to put enemies down in just a few fits, there's no way they can pose a challenge.
My guess is the developer wanted to go in a different direction. Shrift 1 was a very difficulty post apocalyptic game, whereas Shrift 2 is like a playground. Allowing you to experiment and have fun with the Devils. I like it, but I understand the whiplash of going from the first game to this one.