It explains perfectly why Signal does not want third-party clients.

To the haters: I am not saying that it is perfect, in an ideal world we could have secure third-party clients. I am just saying that it is pragmatic: in our world, we don't.

Signal has forever been a pragmatic approach to private messaging, and it succeeded at that: Signal literally put E2EE on the map!

Signal has a threat model, and they do the best app they can addressing that threat model. Which means that they cannot accept third-party clients or federation. They don't say "you cannot use XMPP or SimpleX or Matrix on the side", they just say "we provide this, if you benefit from it, use it for free".

Still, there is a very vocal minority that takes every opportunity they take to explain how "insane" that is, and how they "cannot imagine how anyone with some kind of intelligence wouldn't be revolted". I believe it is the same posture as those complaining about Android or GrapheneOS not giving root access ("even in the advanced settings"). The fact is that if you want root access on your phone, you should install a system that gives you root access, and not select a system that does not and then complain.

Signal is great at what it does. It's okay to also want something else while acknowledging that Signal is great at what it does.