Unfortunately Matrix still has the issue of key sharing between clients. If you want to read previously sent messages when you log into a new client for the first time you have to do the key sharing dance with one of your existing clients.
For me it's a little annoying, but I find it an acceptable tradeoff. However I could easily see how for many people this would be a dealbreaker.
Key backup makes this a lot easier, assuming you've saved the recovery key in your password manager. But it's still one of those frustrating points where it defeats the purpose of the exercise for the provider to be able to recover an account (or at least the content and trust within an account) for someone who's locked out.
For me it's a little annoying, but I find it an acceptable tradeoff. However I could easily see how for many people this would be a dealbreaker.