My operating presumption is that there's runoff underneath market makers for small (on this scale) scalping. I also hope that those who need to return to investors or generate millions/year aren't trading the way I'd be trading to generate $200K/year.

I wouldn't count on it, especially for crypto. The market is brutal. I was playing around the other day with liquidity pools and some bot executed an arbitrage for a total gain of $0.1. That's how efficient the market is.