> I'm drawn to suspect this is just another piece trying to rewrite history to make it seem like modern and less "problematic" authors invented genres we all cherish.

That doesn't work in this case, because the article calls out Lester's early work as 'absurdly' sexist and claims that the standard playbook for fantasy required a male central character. He seems plenty problematic to a modern sensibility. If anything, the opposite seems like a more plausible aim - to claim that Fantasy as a genre is tainted by its sexist origins.