So you're positing that around 6% of people are gay and 1% trans (the Gen Z rates), but that this had such a small effect on reproduction rates that it didn't get selected against strongly enough to offset the new ones introduced by mutation? It just seems implausible to me that a gay man would be as motivated to court a woman as a straight one. The gene fitness reduction would have to be incredibly small (less than a thousandth of a percent) to offset the fact you're only getting a few dozen new mutations per generation in a giant genome where very few of those mutations will make you gay...
Why are you assuming that being gay or transgender would be selected against? Transgender people can have children (especially historically, when HRT wasn't available). Genes can be passed on without relying on procreation of the gay individual - if gay family members increase the overall reproductive success of a family, for example, then genes related to being gay can be passed without the gay persons ever reproducing directly.
Since gayness is prevalent through the animal kingdom, one of two things must be true: it either helps in group environments (whether you choose to interpret that as group selection or "selfish gene"-style counterintuitive effects) ; or perhaps genes related to gayness happen to be deeply tied to some other very important genes that get easily passed on.
Either way, what is your proposed alternative? Do you think 6%+1% is too large a number for historical proportions of gay+trans people?
By the way, 1% for trans people seems to match pretty well the number of Hijra people in India (10M+ out of 1.4 billion). Another piece of evidence that suggests these rates are relatively constant across the world in vastly different cultures.
