I guess the question I'm really trying to get at is "What is the worst that hypothetical Usk can do?"
I think I have a handle on it for Mastodon; the answer is "not much" or it's going to be pretty hard. While the deeply decentralized nature of Mastodon makes it harder to find a good "feed," it strongly protects against this; he'd literally have to seek out the individual instances and start trying to control them, one by one.
But it looks like Bluesky is closer to Twitter (I ain't callin' it X, idgaf) than Mastodon for purposes of what matters to a bad actor. Instances dropping off the map doesn't matter if you have a hand on the control of the relatively centralized recommendation algorithm?