whatsapp/signal/telegram REQUIRE a mobile number to get started. this is a no go from the start for many people, including me personally. i don't care if my chats are e2e if the people after me know WHO i am talking to. the identity is the message and it fails in that test. Second, matrix allows you to set up your own server where YOU allow who comes in, who stays and who talks to other servers, kinda like your own island. none of the others allow that, they are centralized to the core. "signal inc" might not tell the police what you typed but they will tell them when did you log in, how long were you typing and maybe who you were talking to. as i said, that is a big problem because if the police are asking this much about you, they don't care what you said or not.

matrix, well you are the owner of the server if you choose so you get to decide.

signal calls itself "open source" but its not really "free software". the same "open source vs free software" comes up. what i think signal is "source open" and not much. you can't set up your own server, your own client, they are selling centralization as a feature which its not. email has proved otherwise for decades. matrix is what is email.