I think not being able to search for <random celebrity> is a good marker of how mastodon is trying to be something other than just a decentralized twitter clone.
I personally find the twitter microblogging model, wherein most tweets seem to be retweets of high-profile users or comments on their posts, quite unhealthy for discussion among equals.
Twitter is essentially a media site, whereas (I think) Mastodon hopes to be something else, more of a forum for actually taking to people. Whether it can work as/if the userbase grows remains to be seen, but I'm cautiously optimistic.