Twitter didn't really have much of a discovery mechanism in its early years, and that's when it really built the userbase that is its main competitive advantage right now. I'm not sure that's a huge impediment, particularly since Twitter could be the de facto discovery mechanism for people on their way out the door ("Hey, I'm leaving for Mastodon, where I'll be [email protected]").

I do think there's an unmet demand for aggregator accounts on Mastodon right now, though. Like if I'm interested in esports (just f.ex.), there should probably be someone I could follow who boosts significant content related to that subject to aid people in finding new people to follow. (To be honest that probably already exists; like early Twitter, Mastodon is pretty tech heavy. There are a lot of gaps though.)