A server backup is useless if you can’t decrypt it and it’s very easy to accidentally lose the keys for end-to-end decryption. I too have lost my Signal history by migrating to a new phone incorrectly.
The two are not related. Signal has no proper backup and restore, otherwise you could have restored.mulziple times over. It's one of the things that piss me off about signal. Just give me a fucking Backup that I can restore on android and iPhone and desktop alike!
They are related: even if Signal had a backup, you’d have to have some way to recover the key when you lose your device. For example, Matrix does offer backups but you need a key to decrypt the backup if you lose access to all your verified devices.
Without some easy to use out-of-band key backup solution, an E2EE server backup is no backup at all.
But it’s not related to this story. Nobody prevents you from using services that do not operate like signal (and esp with desktop it is now very easy to backup your messages)
Just use those. This is just about whether sth like signal should be allowed to exist.