Mastodon does not need to scale well. Even if the userbase shrinks to what it was before the Big Twitter Exodus (or whatever you want to call it) of last year, it will be perfectly alright.

Mastodon was fun and enjoyable before. It does not need more users to remain so.

It's very similar to how Twitter felt in its early years. You had to know exactly what you wanted to see (topics, people), otherwise you'd feel lost.