The Matrix devs demonstrated an alarmingly cavalier attitude towards fundamental security issues that the writer pointed out in the past, so they are naturally not going to encourage its use.
However, in practice, this was not exploitable: the only way to exercise these primitives was over the network, where network latency and request rate limiting mitigates such attacks.
Meanwhile, we had already rewritten and replaced libolm with vodozemac, a pure rust implementation using robust primitives, shipped in the major Matrix SDKs and implementations like Element and Element X.
I’m not sure this counts as alarmingly cavalier. I do regret libolm ever going into production with substandard primitives from a hygiene perspective, but we fixed it as soon as we could via vodozemac, and meanwhile included the safety warning.
You visibly deprecated Olm after my disclosures went public. When I last checked, only Element and its forks actually use vodozemac, so the rest of the ecosystem which still binds libolm was still vulnerable, and probably still is today.
That's alarmingly cavalier.
I mean, that's the entire issue. There's very little tangibly better than Discord. I like the idea of Matrix, but it's complete garbage in practice.
At least for now, the solution lies more in mass outrage and action rather than any technological migration. The post raises this and I think it's a good point.
The difference between XMPP group chats and Matrix group chats is that Matrix servers replicate all the message history, whereas XMPP group chats are hosted on a single server. IMO the "bring your own account to a central server" model of XMPP is a good thing, but the "replicate all the things" model of Matrix is not.