having multiple accounts has been accepted as the “correct” way of interacting with fediverse?

No. You are right that there should be a better separation between your identity and the servers that you use to connect/interact with the fediverse. It just so happens that the existing solutions have been "good enough" for the majority of people, and there are many other issues (content discovery, reputation, server scalability...) that seem to be more pressing than that.

However, there are some other projects which are on the way to make it possible for people to use one server but have their identity separate. Mitra uses Ethereum wallets as a way to login to the server, while Takahe keeps separate domains for the server and the user's actor ids, which would let you, e.g, sign up with your own id to any server. This would essentially turn ActivityPub servers into a commodified provider, and people could migrate between servers transparently.