Where the metadata goes I think is important as well.
All Signal metadata necessarily goes through Signal’s servers and is tied to your phone number, but not all Matrix metadata ever gets near the Matrix.org if you are using a different homeserver.
I think both are less than ideal in that regard, and I think Briar (strictly P2P) has a much better model for dealing with this at the expense of generally being a UX disaster.
I think shared hosting there is more meant to refer to the older “upload your files in webmin and we’ll shove them in /cgi-bin/ with everybody else’s”-style hosting where multiple users sites are running on a single instance of a webserver versus a VPS giving you a VM with SSH access?