So your point is that you think the claim is wrong? Because, as I've said elsewhere, I think it's prima facie extremely plausible. The idea that minorities are overrepresented amongst the most vulnerable populations, especially when several dimensions of marginalization intersect (in this case adult content creation) is not at all far fetched. Instead it seems fairly obvious.
As such I would put the burden of prove on you when you claim the authors misrepresent their community in order to advance their point.
Now I agree with your point that the fuzzy line is problematic. And patreon can't solve this on their own. I think regulation could, but which politician will stand up for that? The issue the authors have can't be completely resolved in this context, but patreon shifted their policy contrary to how they were marketing themselves to creators before (and what they got good press for). I think that's a good reason to be publicly upset and push back.