Mastodon, Matrix and others suffer that issue greatly. You can't really run single-user instances without running a gigantic installation, when a minimal implementation of their protocols should have no footprint to speak of.
That was the case a few years ago. Matrix' server software has improved a lot since then. It doesn't use much resources anymore. Though there still is a large CPU spike when I join a really large room (500+ users) for the first time.
