I don't feel like anything is really OP, because after Cathedral/Sheol the new bosses are like 10 times as hard and so are the rooms preceeding them.
I dont think you understand
No matter how many times an enemy hit me, i would get heal nearly instantly. If i really needed health i could stand next to the wall and fire, restores a heart each hit.
And I find the final bosses easy, its just the way there is kinda difficult.