Mastodon is more for people who like to have interactions or conversations back and forth with other people, while the big platforms are for influencers/broadcasters and consumers/viewers-- any back and forth interactions there are more between commenters than with the influencer/broadcaster. Of course there is some overlap and exceptions to that characterization, but that’s how it generally seems to me.

So IMO it’s not a competition, there’s plenty of room for both types of SM. Depending on a person’s preference they may use just Masto, just big SM, or use both, each for different reasons. The problem is when people expect Mastodon to be just like xitter/bsky/threads and get upset that it isn’t. Relax and use whichever platform(s) you like.