#Matrix is a protocol, you are talking about an implementation, Synapse on matrix.org, that is slow because 1. Synapse started as a proof of concept and will be replaced by Dendrite and others 2. it has many users and very large rooms.
Matrix is de facto a decentralized database which is transparent with respect to the disappearance or reappearance of nodes, like many colonies of living beings whose borders are bland because they can unite and separate continuously, but maintains the consistency of the data and allows users to interact with it in a granular way with a sort of built-in Access Control Lists.
If you ask me, Matrix is the evolution of TCP/IP Internet in the direction of being more like biological systems. A totally different beast compared to SMTP, XMPP and ActivityPub.