Eh, I've heard this before but I don't really buy it! The reason I don't is because the *experience* of Mastodon is functionally identical to that of Bluesky (or Twitter, or Threads):
1. Download app
2. Make account
3. Search for people to follow
4. Post using hashtags, etc.
At no point is a Mastodon user ever faced with anything involving "federation" or "decentralization" unless they willingly choose to seek it out. It's impossible to tell it from a centralized service.