I've also heard people say this is hard. Then again they said the same for Megaman 9 and 10 which weren't bad at all. Probably helps I grew up with the original MM games.
I admit that I'm not the gamer I was in the 80s but I used to blast through what were considered some of the hardest NES and SNES games of all time in a weekend rental.
Cuphead kicked my ass. I think I got halfway through it. But again, I'm not the gamer I used to be.