The best analogy I’ve found so far is “it’s like having an email address; having a different server after the @ is not an impediment to your participation. Just know that you can only login to the server where your account is set up.”
I’ve been using Signal for what seems like years now.
I’ve got 4 contacts (5 if you include a martial arts school I no longer attend), and only char with 2 of them regularly: my brother and sister.
I’ve downloaded and installed Briar, Session, and Simplex, and keep meaning to test them out with the help of my wife ('s phone) to see what they’re like.
Is this where you come for an argument?