also *as* someone who likes making femMC's to get dicked by futa's I assure you, it's not 2/3rds of the cast though they're certainly much more common than most of the other fetishes except hyper and maybe BDSM.
I think the problem is that how they feel the most satured imo, I don't like futas/herms but I don't necessarily hate them as it's just not my thing, a lot of the chracters that I do like are herms (Frostwyrm, Mirrin, Verusha, Haley, the list goes on for a bit)
They are the ones that feel that get added the most so it feels tad tiring and boring to see new content be "dommy mommy futa that only fucks you in the bun" rather than something new.
Personally I'm tired of the overly muscled characters and the fact that they seem to avoid adding anything to the pregnancy tables unless it's may and even then rarely.
Mirrin come to mind, she can become pregnant but her appearance doesn't change (granted because she is a fucking behemoth of a person) but she almost the only muscled character.
Verusha was planned to become preggers but nothing was ever added sadly.