The problem, at risk of stating the obvious, is that investors are hoping for big returns, and that means big revenue -- and that means changing the definition of "success" on Patreon. To hit a few hundred million in revenue a year and earn their valuation, they're going to need to start competing with not just YouTube and Twitch, but major music labels and indie-friendly TV/film studios. They're going to need to recruit the new Taylor Swift, the new Lady Gaga. Hell, they may need to recruit the current Taylor Swift and Lady Gaga.
The most successful campaigns they have now are bringing in tens of thousands a month, but those are wild outliers. The vast majority of their creators are making side money, not a living; bringing in just $1000 a month puts you in the top 5%. (It's hard to be sure, but I think there's a good chance it puts you in the top 1%, given that there's about 178K campaigns total and there are folks in the top 1000, according to Graphtreon, barely making over $1K a month.) And... that vast majority of folks won't be Patreon's focus in future years. It can't be. (One can argue it isn't now.)
I don't think Patreon will "turn cancerous," per se -- but the Patreon of 2022 may not look that much like the Patreon of early 2020, which some would argue didn't look as much like the Patreon of 2018 as ideal.