“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 Trans*Historical Conference.”
I wonder what would happen at this person’s PhD viva if one of his examiners suggested that, rather than “modern gender norms may not have applied” but actually modern sex-based norms may not have applied, ie women could be warriors and high status, and the whole premise of the thesis was wrong.
You have wasted the last 3+ years, go back and start again.