That's their problem. If their messages aren't encrypted, it isn't like you won't be aware of it. Request that they use a modern client and get with the times. None of this is an actual problem without easy solutions.
Your reasoning would hold up if 80% of xmpp wasn't running on Conversations or forks of it, that all support OMEMO and OpenPGP.
Your criticisms are too broad with few serious negatives. What makes extensions powerful is that they can easily change the rules without breaking the underlying system. If your client sucks, get another?
You have choices, but if your problem is metadata, whoooo boy.
I moved my family group to xmpp to have more personal control over our chats. Signal seems benevolent, but I've seen this play out before. Will it stay that way? We treat online forums with the idea that federstion works to stop enshittificstion. I believe XMPP is a good model for federating secure chatrooms for the same reason: People should control the voices of the people, not companies.
They see no value in it. They don't see that privacy is proactive measure that can protect you.
On Facebook, especially in my family, accounts get lost and hacked. One fine day, it might be someone with more influence in the family who's attacker might make off with stolen bank information or passwords.
I heard You'll die in six months at Thanksgiving one year.
"Really? Holy fuck, I'm immortal! Call the press! Wait, no, I don't want to be locked in a room and tested for 40 years, maybe we all just keep this our little secret."
We're playing Counter Strike, and later, you're in Counter Strike.