@fabio I don't think that libpurple integration is great indeed, I've just mentioned it because you were talking of bitlbee, and spectrum2 is the XMPP equivalent.
Slidge is working on tight integration and is the way to go. And Telegram and Whatsapp are supported (I don't see Instagram though).
My point is that gateway ares part of XMPP ecosystem since the early days, and there are many. You say that you use Matrix mainly for its bridges, and I think that XMPP offer is similar.