Coincidentally I am looking for self-hosted alternatives to Discord for a local community where I live. I have been considering Matrix (one of the Rust implementations) + Element, so I wonder what makes this a better or worse alternative, but there seems to exist no comparison table/chart.

This is a great tool, really deserves more recognition that currently has.

Discord tries to fool with the concept of "servers" which really aren't, Armada is indeed giving full control where data goes and even on public NOSTR servers is kept safe/private beyond doubt.