Cuphead isnt so much hard as it is different.
At least thats Tyler Moldenhauers take on the game he helped create.
We never aimed to make it super hard, Moldenhauer told Variety in a recent interview. It was just that we kind of wanted to keep the action intense and that was sort of the way that it came out.
Moldenhauer sees the perceived difficulty of being more a byproduct of player habits.
Source: N4G PC Cuphead Creator Never Intended to Make the Game so Hard