You're really wrong about that simplex critique. Servers are all self hostable and all simplex hosted servers have onion addresses when you do need to use them (someone sending you doesn't have their own server). offering network layer privacy and decentralization.

A great list of trusted non simplex servers can be found on Nowhere by Nihilist: http://nowherejezfoltodf4jiyl6r56jnzintap5vyjlia7fkirfsnfizflqd.onion/simplex-servers.html

Spin up your own on a vps easily, or better yet behind an onion address only on a local machine and you can talk to anybody with nearly perfect plausible deniability. XMPP simply cannot offer this level of privacy due to it's feudal federation style of decentralization. 

Daedalus

bitcoin

"I'd quicker abandon bitcoin and go back to fiat!"

jasonb

my mistake I thought you meant Signal. 
What is so good about simplex and xmpp?
As a company Simplex is inherently centralised and thus prone to state requests for data.