alt Hacker NewsIRC definitely is not E2E in practice. Matrix hasn't reached feature parity with discord at all, unfortunately (and the main server has a big spam problem for any public chat. not to mention a publicly accessible chat and E2E are kind of a contradiction in goals).
I am sure popular public Discord servers get their own share of spam, but with Matrix you can host your own, or join one of a friend you trust. That is what freedom looks like. E2EE is optional.
OTR supports IRC, but in practice either solution beats the privacy of Discord, which requires all traffic to be sent in plain text to their corporate owned databases.