Signal is E2EE encrypted (similar to Telegram’s secret chats but probably better) so it’s less vulnerable. If people know about it they can ask Signal to ban you, but they can’t just passively spy on everything.
That said, XMPP is better still IMO.
(Edit: centralization isn’t as big a problem as you might think with Signal. The wealthy own the whole world now. You can’t set up somewhere outside their jurisdiction, you can only stay ahead of them as they force people to stop hosting you. Sending a takedown to Signal is the same as sending it to your hosting provider, do not fool yourself. )
They could turn on end to end encryption and the fact that they aren’t doing that is telling imo.