You're right, he's not a professional historian. And that's a good thing, because History the academic field is hopelessly sick and outdated.

Turchin may not be right about everything (or most things), but the kind of thing he's trying to do is the path forward. The really interesting action in history (broadly construed) is all being done by people doing history within analytic paradigms, like Turchin. Look for work by people who call themselves economic historians.