I agree that player-sexual companions need to be undone. I have never (and will never) subscribed to the belief that the artist's job is to "please the fans." Here is my case for why it is bad that companions are player sexual.
#1. People in the real world have preferences. In some cases these preferences are very strong, in others, less so. If it was "just so easy for everyone to change sexuality" then downright unethical practices such as conversion therapy would have worked and been considered a success. Newsflash - they were not and I think almost everyone can agree they were a monumental failure. #2. Creating a world in which all of the companions are player sexual undermines this. It reduces the depth of characters, in order to potentially not upset the group of people who want to romance that character who would otherwise be locked out of it. #3. By making it, "easy" for everyone to get along/romance each other, its not only not realistic, it is actually in some ways an insult to those who have had to struggle through those kinds of situations. Overcoming a personal prejudice is not easy and it does take time. Making it easy takes away from that. #4. By giving characters defined preferences it adds that extra layer of depth to companions and makes them more "real." Viconia in BG 2 for example not being romanceable by an Elf made perfect sense in the context of her story. She has deep, racial prejudices against elves. Likewise, Shadowheart should feel the same way towards a Githyanki PC. Likewise, there should be strictly gay companions, as well as strictly straight companions. #5. The purpose of people within the world is not to please you. If you go about in the real world and expect everyone to like you, or expect everyone to want to sleep with you, well, I think you will get a wake up call very quickly. I do not see why this expectation should suddenly exist within a fantasy world. The purposes of the characters within the game should not be to please you, they should be there to tell their own story. A well written, convincing companion is one who would seem to be their own character and not seem to be defined according to what you have done. They would have some prejudices that you would be unable to change. Its perfectly fine for the canonical ending for a game or a character to be one you do not like, because its not your story.
I do not believe that all the characters need to be gay, nor all the characters straight, nor all the characters bisexual, but if a character behaves in all of their dialogue to NPCs as if they have a certain orientation, that should not magically change when talking to the player. Asterion very much comes across as straight for example. He spends a lot of time hitting on female characters, but he does not provide the same attention to male characters. If Asterion is not straight, he needs a pretty damn convincing reason as to why he behaves differently to the PC in contrast to how he reacts to the rest of the world.