I think we're on the same side doedoe.
I'm pointing to the anthropological finding that "third genders" are more prevalent in highly patriarchal societies with rigid sex-stereotypes and gender roles (in the old fashioned social sciences sense of gender). That's just an observation about how human beings relate to one another within cultues, and how the overall patterns of those relationships vary from one culture to another.
One might then hypothesise, based on that observation, that this indicates that the existence of third genders, being so variable across cultures, is not evidence that "trans people have always been with us and being trans is innate", but rather, evidence that phenomena which might be interpreted as "being trans" are sufficiently culturally variable to suggest that culture and social construction play a massive part in their prevalence, rather than being "natural".
To this, I personally would add a value judgement, namely that third genders do, as you say, seem all about re-inforcing sex stereotypes and gender roles, with the primary goal of keeping women subservient and second class citizens, and that this is clearly a bad thing.
So yes, I think we're on the same side here - I just want to use anthropology to point out that the way the current western European/North American trans ideology co-opts and appropriates "third genders" to defend a simplistic view that "being trans is entirely a biological things which is always there" is not plausible - because prevalence of third genders is highly variable cross-culturally and historically, and there is a strong correlation between the existence of third genders within a culture and that culture being highly patriarchal and having high degrees of inequality between men and women.