I think "is X the next Twitter" is the wrong question to ask.
When I started working at Twitter (now years ago) my relatives asked me if they should join. And after thinking about it, my honest answer was "no". The only person who needs to be on Twitter is somebody who wants to feel like they're part of a global conversation. Most people just don't and won't.
Twitter is only successful because it started in an era where that was a novel and appealing idea, and because it developed a critical mass of users. Both traditional participants in that conversation (journalists, politicians, media personalities, etc) and new ones (like dril) came on board. It is now gradually losing that critical mass.
These days there are just too many options tuned to too many sets of needs. Mastodon will get a chunk of those people, as will existing social media properties. But I don't think we'll ever again see a global groupchat at the scale of Twitter. Assuming Musk persists in running it into the ground, I think in a decade's time Twitter will be in that bucket with MySpace or SixDegrees, one of those early-internet things that people remember with varying degrees of fondness but would never go back to using.