In regard to Reddit having the same problem, I agree it does to an extent. But like you said, it only allows for synonyms or alternate wording for the same topic in a subreddit’s name. On Lemmy, since instances are different, the fractured communities can be named the exact same thing. Most casual users are not going to realize this and think that the one community they’re in is not active when on another instance, the other like-named community might have grown and is now quite active since they initially setup their subscriptions. They’ll never know unless they happen to run another search and see the alternate community’s user count.
Maybe I’m wrong and it isn’t a big deal. But I do agree that searching and indexing would be a great step in helping discoverability.