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.
That doesn’t mean anything. If you have tons of free RAM, programs tend to use more than strictly necessary because it speeds things up. That doesn’t mean they won’t run perfectly fine with 8GiB as well.