There's no UX sacrifice in my Chirper scenario. The assumption is that Chirper has parity with Twitter on all UX and all content, as well as having lots of exclusive content.

Re Joe Rogan losing listeners: my claim isn't that each individual prominent tweeter will keep the same amount of readers, it's that Chirper will be able to financially incentivize many prominent Twitterers to tweet exclusively on Chirper in exchange for taking on some loss of readers (note that they can massively overpay since they just need to reach a tipping point and network effect, not really think about unit economics), and then Chirper will have more reader market share than Twitter. Spotify currently has successfully gained more market share than any other podcast player, and they haven't even touched the set of podcasts I listen to. If they grabbed a couple of the podcasts I listen to, I'd switch from Overcast to Spotify.