I just found the original post and I slightly disagree. I think their end goal with the decentralization shit is they want decentralized but centralized.
Look at Bluesky and how the network architecture is "centralized" in a way. Look at how Eugen tries to corral people into a few instances that share his viewpoints and how they push blocklists. Aside from easily being monitored, it also allows them to control the flow of data. Look how Meta and Mozilla and others are getting in on the game, they want the same thing or similar goals, be it censorship or monitoring or both.
They don't need to take over much to create an e-mail issue, especially if instances on the freer side have signups turned off.
https://cfenollosa.com/blog/after-self-hosting-my-email-for-twenty-three-years-i-have-thrown-in-the-towel-the-oligopoly-has-won.html