I've been saying this from the go: users don't need to know decentralization even exists until AFTER they are signed up.
What Mastodon needs is a proper migration flow that moves old posts and remote follows so users can decide if they want a new instance after they spend some time in the system and start to understand how it works. Any mention of decentralization on signup is a churn point, because decentralization doesn't add any features to posting and reading posts. From a UX perspective, decentralization isn't a feature.
Things are about to get messier once the big decision coming in becomes "do you want to see Threads or nah?", which then actively requires thinking about a competing social media platform on the way into this one.