Being in alpha and having breaking changes is fine, the question is how many. My impression is that Immich seems to introduce breaking changes far more frequently than what people might be used to from other projects.
And that does go back to professionalism: The better you plan ahead, the fewer breaking changes you have to impose on your users.
syncthing also relies on a web server for device discovery, it’s just that you’re probably using someone else’s server instead of hosting your own.
Correct me if I’m wrong, but I also think that Vaultwarden itself doesn’t have access to the unencrypted password database. In that sense it’s E2EE similar to KeePass, the only difference being that KeePass is a desktop app and Vaultwarden a web app.