So, I'm replying mainly to his assertion that any interactive app can be prerendered on the server given current technology. Given webapps span the range from "dynamic forms" to browser video games, I can think of no way of implementing the full breadth of what are modern web applications other than essentially video streaming and polling input on the client, which yes, is bandwidth intensive.

That's the entire reason why js and html and friends have become so popular. You essentially have full applications that have been developed by people who recognize that the bottleneck wrt to a networked application's responsiveness is not cpu cycles and memory in 2015 but internet latency. It's sufficient here to send a small text file and have the client fill in the gaps and have the client ajax for updates than have the server do the heavy work. I think you argued elsewhere, this is a waste of processor time redundantly rendering content, and thus, a waste of energy needlessly (as in real energy, from electrical into waste heat). As a tree hugger, I have to admit I find that argument somewhat compelling. I think a balance needs to be struck between user experience and use of resources. It might be your balance line lies further towards the "saving of resources" than mine's does.