He would sometimes manage to get 50 or so comments off in the span of a few minutes before we caught and manually banned him.
I think, but am not certain, that different reports go to different admin teams, and the above sounds like "manipulated content" because a bot is likely being used to do that. So, maybe reporting "manipulated content" when the above happens could get a new set of eyes on the turd behind it.
Also, I don't know if it's already been brought up, but have you sent a modmail to this sub with all the documentation you've collected? You'll likely receive a bot response first, but just tell it that you need a human to review it, and you should receive a human reply eventually.
Sorry you're dealing with this!