Optimistic UI probably isn't necessary for a web site, but you'll certainly want it for a web app (which is what Htmx claims to be good for).
In the real world on the mobile web we actually have, TODO apps (which is what TFA is about), calendars, notes apps, etc. all work better with client-side state synchronized to the server in the background.
React has a bunch of good libraries for this, especially TanStack React Query.
Htmx doesn't.
Hah! Good luck getting React even to start up in that environment. Meanwhile oldschool HN will still be snappy. Speaking from experience.
In my experience optimistic UI updated don't actually make much sense if you expect users to regularly see large delays. Optimistic updates are great though to avoid the jank of a loading state that pops in/out of view for a fraction of a second.
> It's basically the speed of the network.
Does your stuff work on mobile web? Mobile web requests can easily take seconds, and on a dodgy connection, a single small request can often take 10+ seconds.
The difference between optimistic UI and non-optimistic UI on mobile web is the difference between an app that takes seconds to respond, on every click, and one that responds instantly to user gestures.