Not “not ugly” either. The flexibility is too high and standardization of UX is too low. Technically, we’re missing adoption of default standard toolkits like swing or GTK, and politically a11y/compliance checkers are a far cry from something like the HIG of old.

How so?

You can make slow things with it of course but it's not inherent.

That depends what is build and how. Granted that a modern web browser is indeed an order of magnitude heavier than an OS, once that ticket is paid anyway, one can built very far, without relying on any additional bloat that contemporary web frameworks puts on top of it. There is not that much more data to send though HTTPS to bring a far more convenient UX than what raw text bespoke tweaks can offer over SSH.