In some way the developer is right, all the fetishes are "optional" but something that the dev never said is that the girls are "optional" too, because if some girl is into watersports or some fetish that you don't like, you lose your chances with that girl because looks like this girls are only interested in one fetish and all of them are only interested in one at the time, so you lose the chance to see all the content that those girls have, still, don't worry because they don't have much or interesting content, all the content those girls will give you is only related with the fetish they like, so most likely you will end fucking just with 3 girls of the 20, and avoid all the others because the game force you to choose those fetishes just to fuck that girl.
Later in the game the dev doesn't even care if you like something or not, if I'm not mistaken there is one scenes with Lysa where she gives you a footjob, I don't like footjobs and I'm pretty sure I never said that I was okay with that, but the game still make it happen, if you see the script there are options that give you better outcomes with some girls, but those options are fetishes, like a rimjob, so to get a better relationship with that girl the game wants to force you to choose the rimjob.
I was kind of okay with the game at the start, even when was pretty clear that the dev lock you out of some girls paths on purpuse when he made them fetish exclusive, but later in the game that is more noticeable and worst.
Im okay with optional fetishes but not with "optional" girls, that is stupid.