There's a slight (see, big!) difference between speculative fiction (which is what Star Trek is) and historical fiction (which the example that you use).

This Star Trek was a imagining. Being a Stud/Slut doesn't mean that this Kirk had to remain completely straight. It wouldn't have changed the essence of the character, imo, because Kirk wouldn't commit to anyone in any event... in the end it's zero-sum.

But representation is still important.

It would be nice to see other characters get their thing on, but I doubt that will happen, the focus will always be on Kirk and Spock (maybe Bones... but it's not a troika yet... looks to be Uhura this time around).