I couldn't be less interested in arguing with you about Signal. My point is that it doesn't make as much sense to compare Signal and Matrix as people think it does. Large-scale group chat is intrinsically less safe than the kind of chats most people use Signal for. You can substitute whichever other secure messenger you prefer.

This "average nontechnical user" stuff, though, miss me with. For 2 decades people have been encouraging the "average nontechnical user" to do incredibly unsafe things on the premise that any kind of message encryption is the best alternative to sending plaintext messages. No: telling people not to send those kinds of messages at all, unless you're dead certain the channel they're using is safe, is the only responsible recommendation.