The use of XML is a bit unfortunate, but these days there are a huge range of mature XML libraries for any language, with a variety of different styles of API t

The use of XML is a bit unfortunate, but these days there are a huge range of mature XML libraries for any language, with a variety of different styles of API to suit the programmer / program design, so the use of XML doesn't really affect implementation that much. Not to mention there are decent XMPP libraries for many languages, so only the application-specific logic needs to be implemented. XMPP has a clear design based around general concepts, that make it useful for a wide variety of messaging-type applications. The criticism I hear often seems to come from people approaching it as an IM protocol, and then being upset that they need to learn some general XMPP concepts to understand how IM is implemented on top of XMPP. The reality is that it's a general protocol, which can be used to implement a variety of different real-time messaging applications. That generality can cause people to think it's overcomplex if they approach it as if it's designed purely for IM. You'll often find XMPP as the underlying tech for IoT real-time communication, or for signaling/presence (as an alternative to SIP) for videoconferencing (for example, Jitsi Meet uses XMPP for signaling). In this way, XMPP is quite widely used, but often not in a way that people are aware of. By contrast, Matrix appears to attempt a clean-sheet design without learning any of the lessons of the many protocols that came before it. The protocol is heavy on special cases, has many serious inefficiencies (many coming from an apparent desire to make the protocol "more Web"), and especially on the server side requires a large amount of implementation work simply to get to a basic level of functionality (as opposed to XMPP, where a simple server for a basic set of functionality can be written in a very small amount of code, especially if you make use of an existing XML library). I've written code for both protocols (as well as many other protocols with similar goals) and will do my best to avoid touching Matrix ever again.