You forgot Themestream, Red Paper, and The Vines. Not that I blame you - it's hard to even find some historical trace of them, these days. And this is exactly why. Humans are much better at gaming a system for ill-gotten gains than for working at it.

Maybe Medium should require a certain number of well-vetted articles to be published before an author is allowed into the MPP, and if their overall content dips after that, they can be knocked down a revenue tier or removed from it altogether?

My daughter and a good friend expressed similar frustration with classmates in university graduate level programs. I never patted my kids on the head and told them their writing didn't need improvement - my daughter used to toss commas around like confetti. But they're both excellent writers, today. Not "by comparison to their peers," but in their own rights. By comparison? They're Pulitzer Prize material. :)