Matrix is even worse.
- https://raw.githubusercontent.com/libremonde-org/paper-research-privacy-matrix.org/master/part1/README.md
- https://raw.githubusercontent.com/libremonde-org/paper-research-privacy-matrix.org/master/part2/README.md
- What happens when a Matrix server disappears?
- Matrix notes - anarcat
At least OMEMO supports forward secrecy so that would put XMPP above both Element and Session.