Yes but I'd say some people (me) like WhatsApp because of the privacy and end-to-end encryption. Email i assume is less private but still more private than a public post.

Imagine someone puts all the Signal messages someone else sent them through an AI. I dunno. I think problem is most AI doesn't work like Confer.to, also by Signal's founder.

People have been screenshotting conversations, saving them on their phones, and sending them to friends over text for as long as there have been conversations to screenshot.

The entire concept of conversations being "secure" is only as good as your ability to trust the other party isn't doing something insecure with them (and that yours and their devices are, themselves, as secure as you think they are. Which they generally aren't.)

All of which is to say, it's security theater and always has been when applied to real life situations.