I haven't seen Urbit advocates contest the things he's saying (and he's not the only one that's said them). They'll say "it's a work in progress" or "that's not what were trying to accomplish" or other deflections.
A cogent retort would advance the conversation, but it won't happen because what he says is largely correct.
I think the people working on Urbit have learned that it is not productive to engage with the HN community. If you view the previous discussions (going back years now) it rarely goes beyond "hoon is intentionally obscure" and usually devolves in to CY politics bashing (e.g. see current thread). It is safe to say that Urbit is the most hated project on HN.
It is unfortunate because we need more weird projects out there, and less articles on javascript framework updates. Given the state of the web and social media today, I think we would do well to encourage projects like this and others like them. Or we can just all download MS Teams, live with FB and uBlock Origin, and say it's all good.
Well, would you consider someone who'd only spent a couple of hours of wall time on Unix to be an expert whose opinion was worthy of serious consideration?
Not that I'm flogging Urbit -- or not flogging it, for that matter. I looked at it a while back and decided that I didn't understand it, and wouldn't understand it without spending far more time than I had available. However, that just renders my opinion on the topic useless.
I would encourage them [= someone who only spent a couple of hours on Unix] to dig further... broader. Mostly by demonstrating that there are real world problems for which Unix is better suited than competition.
IMO in Urbit -- there was not much more to explore after the few hours. Short of digging even further into the guts of it... and that was very unappealing.
Other people here in the comments mentioned that there's no killer app for Urbit. So my intuition was probably correct [to stop digging].
A cogent retort would advance the conversation, but it won't happen because what he says is largely correct.