I know this isn't the answer you want, but I sell people on Signal based on the user features. I’ve had great success in getting my friends and family to adopt it.
Signal is incredible user friendly, privacy respecting, the gold standard for encryption, cross platform, etc. Yes, it’s centralized, yes it’s imperfect in many ways, but it’s easy and it’s pretty damn good.
If you want to help the people around you to become more involved in understanding and owning their tech, it has to be an easy and good experience. It has to be tangibly better, not just abstractly better with tangible downsides.
I use XMPP, but would never try to convince my friends and family to use it; it’s too complicated, the user facing apps all suck (Snikket and Cheogram are the best of the bad lot), and the incentives to use it aren't there. As you said, it’s just not attractive to a regular user, since it’s all around a worse experience than what they currently use. The one exception is that I do occasionally recommend XMPP for SIP access via jmp.chat to some of my more technical friends who have a tolerance for clunky user experiences in favor of privacy and affordability. I am holding onto an unreasonable hope that Signal or Whatsapp or others will consider XMPP+OMEO in the future to popularize the standard, but that is extremely unlikely.
Matrix also is an unfortunately terrible alternative to discord (even Element is a rather lacking user experience), so while I have pushed to move groups there before, I no longer recommend Matrix. I suggest signal or nextcloud as alternatives when possible; the remaining large groups who need the closed server forum style system are usually unlikely to move to Matrix anyway.
Signal is a non starter for me. Centralized, requires everyone that uses it identify themselves, and they can and will use it to shill their crypto tokens or any features they want and you have no say. Its no different than Whatsapp to me.
If I cannot host it myself if I want to, or use it anonymously if I want to, then its not sovereign tech and not worth a second of my energy convincing anyone to use, especially when sovereign alternatives exist.
Matrix is by far the most usable sovereign option so it is what I switched my personal network to.
I have gotten all my family and even inlaws onto Signal. (It helps that it lets Android users send higher quality pictures than SMS to iOS users, while not being social media like Whatsapp, ie. great for groups that include kids.)
But I can't even decide on a matrix/xmpp client for myself, much less for family or friends.
Yep, this is the insight that so many ideological purists are missing, in the privacy space and in free software more broadly. A 90% solution that "just works" is infinitely better than a 100% solution that nobody is going to use.
In my mental model, Matrix (specifically Element) is decentralized Signal. In other words: a modern encrypted messenger that is protocol-based and so allows users to control their data if they so wish.
If this picture is accurate, then the promised land is only two steps away: (1) make available a reliable default Matrix server for normies who don't care about privacy; (2) polish up the UX of Element.
What am I getting wrong?