Being bland has nothing to do with sexual orientation. Being straight doesn't make you interesting.
As for the NPCs, they aren't real people. They should be convincing, but its the player that matters. Just because an experience is uncommon doesn't make it invalid. Live how you wish, and grant others the same freedom.
What makes you interesting is having a defined character with likes and dislikes instead of jumping into the bed with everyone and everything as long as it is controlled by the player. For example a companion who has a dwarf fetish and would only romance them (and male gnomes if they have a beard) is much more memorable and interesting than the current sex robots.
To you, others may disagree. In fact, others will invariably disagree. The aspiration of any role playing game is to make a shared experience as attainable to as many different people as possible without diluting the content and bring them as much joy as possible in it. Sexuality is a matter of preference not importance. Whether someone is attracted to their own gender or the opposite has no bearing on their qualities as a human being, it is no more significant than any other matter of taste and appetite, whether it be a question of music, food, or fashion.
These are personal expressions but it is ultimately the person that matters
No, this isn't a game to make one character and have them experience everything.
fighters are not rangers are not clerics are not rogues.
You want the fighter dialogue unlocked, you roll a fighter.
Shadowheart already has githyanki specific options.
The experience, if you wan the other locked options, is to make a new character, and play with it.
You want a movie to just show whatever romance you want?