Most people seem to not want to be discoverable with the exception of artists and other people who want to make money, I doubt search will replace hashtags as the primary discovery method
Aren't searchability and discoverability two different things? I understood hashtags as a way to make your post discoverable, or more accurately, to comment on a topic that there's a consensus term for and so everyone can see your opinion. If I was looking for a specific opinion, some piece of news that I remembered a short sentence from, then I would search for the phrase I remember.
You could make the argument that they're technically different things, but I think in practice they are the same. If you're looking for something specific, then yeah search is gonna be more effective than hashtags. But if you're just looking for something to read, you could search for "fediverse" or trawl the #fediverse hashtag. Not everybody chooses to add hashtags to their posts so full text search is gonna find more posts than just a hashtag search (assuming full text search also returns matches on hashtag).
I use hashtags on my posts to help other discover them, but also to group my posts by subject. I probably follow 30 different hashtags on Mastodon to help me find interesting posts.