Well, saying everything is biology is either something of a truism (because of course humans are living beings, etc.) or a very strong assertion (because either it excludes environment/culture or collapses it into biology). In the meanwhile, we do know that gender is not always the same everywhere, that different cultures and groups use different categories, and that these are understood and organized differently. Even if (I won't deny that) biology is a factor, we don't know how it operates, and in any case, it depends on a specific system of gender to operate on individuals.
And what you say is exactly what I ask for: replacing trans-like experiences within their context. If we don't do that, we run into methodological issues and ethnocentric/colonialist tendencies.
All the same, you're not really answering my only positive claim: "What is more useful than looking for trans people in the past is to look for different understandings of gender, in different places and time, and to look for the transgression of this particular system by people who lived in it." It's not really that different from the OP. It's the same project, without the universalizing tendency.