Matrix is definitely closer to Discord / a platform built for communities.
SimpleX is not P2P, as I understand it messages are forwarded through a random(?, at least varying) number of servers, so no server knows the sender and recipient. The main issue it attempts to solve is a complete lack of a persistent identifier. Your “account” does not have a single address you can be messaged on (you can create ephemeral ones). You can create a new identity for each person you message, meaning you don’t have to trust the people you’re messaging to keep your messaging account’s ‘identity’ secure.
I also really like how easy it is to route through proxies (esp on Android)