Perhaps I should have avoided the word fetish, it is perhaps a little too negatively loaded, but I can't think of a better way to express the kind of sexually loaded fanservice it appears to me as. The act of making characters player-sexual reduces them to vehicles for the player's sexual fantasy in that aspect.
I think it depends on how the characters are written. Any character COULD be written as merely a vehicle for the player's sexual fantasy, even if they had a fixed sexuality. But you could also write rich, detailed characters with much more to their personality and their story than the romance aspect, and then they wouldn't be that.