> Someone else centralises the data and you have to trust them to keep it safe. Email doesn't have this problem because I can take my emails elsewhere and/or change my address, something I've done plenty of times.

I'm not going to defend any social network, and I think that in essence you are right; but using email is a terrible idea.

Is just that people don't understand email any more

When I've been added to a email chain (last time at the end of the 2010s), it was an awful experience: you can't get out, people including addresses in "To" so they get added to all recipients address book (they keep a copy of each email, security depends on each user of the chain!), windows users get infected with viruses and you start getting those as well, nobody will remove anything from the emails so you get huge emails with top-posts without context on what they are replying to, ... it was a mess!

I have no reasons to think things have improved.

So perhaps a better email is needed, and I wonder if it may look like a social network.