It depends on how many characters there are that can ntr the mc, i'm assuming there will most likely be more than just yasuo doing the ntr,as in one the preview pics there's an unintroduced character with the wife,and not to mention all the monsters.
So if you think about the mc being one character vs all the multiple other male characters,even though he is the main one it would make sense for those characters together to have a higher amount of content then just the one.
So yes turning off ntr disables like 3/4 of the games content,but that doesn't mean non ntr path will lack content...I mean what the heck is the mc suppose to do after fucking every woman in town,he can only have so much content xD