they found trans vikings

When you point this out, you inevitably get hit over the head with the "but trans people are so rare!" argument, which completely ignores so many counterarguments. Even if we assume trans people only make up around 1% of the population, that's not rare. That means there's one or two in every normal-sized group of prehistoric H. sapiens sapiens, as these were typically about 100-200 individuals. For comparison, complete heterochromia is more than an order of magnitude rarer, albinism is just one in 20,000 individuals, and even that is still a lot more common than the really obscure genetic variants. The assumption that trans people are rare is based on not understanding in the slightest what counts as rare in human genetic diversity.

And that's just a comparison to the entire population as the baseline, which is ultra flawed to begin with. When we're talking the actual likelyhood of transness being the explanation for a person's burial site being so full of markers of a masculine gender presentation that everybody assumes that person to be a man until it turns out the body had XX chromosomes, we have to draw a comparison to how many cis women are so gender nonconforming that literally anything about how they present is masculine coded. As somebody who spends all of her time in queerfeminist spaces, i come across a ton of gendernonconforming people and that somebody that masc-presenting is actually cis is at least as "rare" as that person just being transmasc in some way. Obviosuly neither is by any means unheard of, but there really is no reason to default to "that person must be totally cis" except the epistemic erasure of trans people.

Yeah, sure, that culture has almost certainly done gender in totally different ways than us. There's a lof of historic and contemporary examples of societies that just sorted everybody who nowadays would be called queer either into a catch-all third gender category, or into the "opposite" of their AGAB. There's at least one culture around today were both of these approaches are traditionally an option, the Bugis on Kalimantan. But these results are not treated at all as if we're talking about any of these societies. Cisness is assumed to be not only the null hypothesis, but the only possible explanation when there is actually zero reason to do that.

shaperson