The theory has been put forward by James Davison, a PhD candidate and tutor of medieval history at the University of Liverpool, who also convenes the TransHistorical Conference.*
So Mr Davison has skin in the game and a conference to sell. Colour me shocked.
No, you absolute effing numpty, having women warriors and men sitting around eating bonbons doesn't make anyone trans. It means gender roles vary through cultures and eras, which anyone with half a brain would know.
Trans is a recent cultural invention. Gender non-conforming is a tale as old as time, and does not need retrofitting to squeeze into new ideologies.