There is nothing wrong with putting a jump scare warning. I'm not even saying that they should or they shouldn't. I'm just saying that some people feel more comfortable knowing what they can expect from the game and that is something that developers can choose to respect or not.
Requesting that games should have a 'jumpscare' warning is absolutely valid criticism. It's up to the developer to decide whether or not they'll act on that criticism and it seems that they have so it doesn't even matter what we think at this point, I'm not sure that it ever did.