So, it’s plenty good enough for them.
Yeah, but on the other hand, you can’t even log in normally to a Matrix/Element account. I mean using username + password. It’s not expected that you ever log out or lose your browser session. If you do, you must use a one-time backup code (that you must create and save beforehand) to log in again.
To be fair, I can’t say that I fully understand what Matrix is doing in the first place. The text that I quoted reads like they have your keys. But they also claim that they only store this stuff encryped: https://element.io/en/help#encryption5 So … encrypted with what? Only option here is my password, isn’t it? (But if my password was good enough to reclaim an account … why do all the other stuff …)
Matrix takes end-to-end encryption seriously. When I ran a Matrix server for the family, the family members would regularly lose their keys, because they didn’t pay attention to something. That’s on purpose! Or rather, that was on purpose. Maybe it’s different these days?
No clue.