besides that, and besides the lack of forward secrecy on matrix and session already mentioned by privacy guides, do some of these alternatives have worse security, privacy, or ux than signal in some way?
Matrix also does have a pretty big problem with meta data. By default it stores a ton of meta data (at least the reference server implementation does) and I am not sure if this is even a solvable problem without redesigning the protocol. When opting for an alternative to Signal, XMPP is probably the better choice.
besides that, and besides the lack of forward secrecy on matrix and session already mentioned by privacy guides, do some of these alternatives have worse security, privacy, or ux than signal in some way?
Matrix also does have a pretty big problem with meta data. By default it stores a ton of meta data (at least the reference server implementation does) and I am not sure if this is even a solvable problem without redesigning the protocol. When opting for an alternative to Signal, XMPP is probably the better choice.