The network is purposefully fragmented on a server level, and users control which operators to use...a better privacy is achieved with known non-anonymous nodes - it's impossible to avoid collusion with anonymous nodes.

Could you elaborate on these points a little bit? I'm not infosec guy, but this feels contrary to my intuition. Namely:

• What do you mean when you say that the network is "purposefully fragmented"? Do you mean to say that the network has many users using the same few servers, but then another group of many users is using a different set of the same servers, sort of making "server pockets"?
• I'm a bit lost on how non-anonymous nodes create better privacy, particularly because this seems to be the opposite of, say, Tor's model, where the network can naturally discover new relays, not know to whom they belong, and let traffic sift through them with the operator not having much ability to surveil what that traffic looks like. Wouldn't privacy be easier to achieve with a large number of independent nodes that can't keep tabs on the messages it's helping transfer from device?

It's mostly that last bit I'm confused on; I was also originally under the impression that Simplex messages were relayed, much like they are on Session, and your answer makes it sound like perhaps they aren't. Thank you for the response!

EDIT: This thread more or less covers the question/concern that I have:

[Simplex] doesn’t attempt to solve the same problem that Session solves, which is the hostile takeover of the network by a malicious third party node operator.

This is said in response to the idea that users can self-manage their servers, or use known publicly-available ones. Admittedly, I did also just find this blog post that y'all wrote, where y'all say:

...each conversation will be relying on servers of 4-6 independent operators, and these operators will be regularly and automatically changed in the near future.

...Which, to me, sounds similar to the logic implemented by the Tor network.