I think I have a theory on why almost all, if not every, human/fire gub is a female.
So we have seen that gubs like chickens, weasels, cows, and goats have evolved drastically from our present earth counterparts. Who's to say that humans haven't too (just mostly internally)? They way I see it, humans have possibly evolved to be primarily female in two ways:
They have evolved into a colonial species like past ants, wasps, and bees. Meaning, there is a main "queen" that makes "workers" (most of the humans we see) and only a few males for reproduction purposes. This could also explain the human with the special exoskeleton as some ant species have specialized workers like supermajors.
They turned into an asexual reproducing species (meaning each human can reproduce on their own and has removed the need for sperate biological sexs). This development would cause every human to have an uptick in hormones such as estrogen in order to be able to reproduce on their own, causing them to all be, or at least look like, they are all female.
So what do you think, did I hit the nail on the head, was I close?
I'm afraid that's spoiler territory, but good work! You're not far off.
(Though, Vera doesn't have an exoskeleton, she's just wearing a suit.)