For the Seekers, though, they say that tias who go out to form their own tribes are extremely rare and the successful ones are even rarer. Ousting a male in a different tribe is also never mentioned anywhere in lore that I've ever seen? And it remains the case that we have two distinct lore sources that explicitly state that they have fewer males, biologically, plus the other less explicit cues.

Also 1.0 had fewer than 5 male miqo'te NPCs in total, and one Ul'dahn NPC back then used to remark that he'd never seen a male miqo'te in his life and he wasn't sure there were any in the city at all.

So it seems overwhelmingly likely with the evidence we're presented that they are in fact rarer, and the hypothesis that it's purely cultural/selection effects with no biological ones whatsoever seems to have no particular evidence in its favour other than "that's how it seems to work on the First".