I find the game not very difficult, especially because some power ups do become busted (dash bypassing mobs, invincibility bypassing the spiky dungeon area , shockwave clearing all mobs on screen).
And I do want it to be difficult because I want to get those delicious game overs without playing bad on purpose.
That being said, I agree that some bosses have too much HP, and some bosses ramp in difficulty to the point of nonsense
(Mausolea overwhelms you with spawns and flies all over the screen, gives you no time to slash back at her. The Witch to the lesser extent, still too resilient, but at least she gives windows to attack her. On the other hand, Werewolf needs to be tougher~)