OP is appealing to logic, but I find many if not all of the arguments to be logically flawed.
For starters, it’s important to recognize the difference between decisions made for gameplay reasons from those made for lore and world building reasons.
Your companions aren’t really all bisexual, they are playersexual. That’s a simple gameplay decision Larian made so that anyone can do the romance thing with any character they like, regardless of their character’s gender. There are valid arguments for and against this approach, but it’s not uncommon, it’s just about giving players options. Outside of your party I can only think of a couple of obvious gay relationships, and one of them is more notable for being between a mortal and an immortal.
Racial ability modifiers were probably also removed to simplify character creation. I don’t know how much difference it would really make when you can just add and remove points anyway? I guess you could make an elf with a starting dex of 18 or something?
The female warrior complaint doesn’t really work either IMO. The real world reason that women tend to not be as strong is because human evolution means it’s the women who have to deal with pregnancy and childbirth. That’s not the case with Githyanki, so there’s actually no “logical” reason that Lae’zel shouldn’t be every bit as strong as male counterparts. And Karlach has been experimented on to turn her into a literal war machine. These are both cases where the fantasy element is just more significant than arguments you can carry over from the real world.
As for racial diversity, again in this fantasy world, we have humans, elves, dwarves, gnomes, halflings, orcs, goblins, etc. which are all far more significant differences than the colour of someone’s skin. In this fantasy world, prejudices and rivalries between the different (fantasy) races probably would far outweigh what we consider racial differences in the real world. That would likely mean that they’ve been traveling and mixing freely throughout their history and no one would bat an eyelid if the grand duke of a city happened to be a black man for example.
TLDR:
Being a fantasy world and being a game really does explain these things.
