I think we might agree with each other, but you are being more clear than I was. If we are looking at the web as the miraculous document-exchanging network that it was, yes, Javascript is may be literally ruining everything. If you can render something once, absolutely do it once, what a huge waste.

I was more disagreeing with the concluding assertion that "with modern tools, there's no reason that anything — even a highly interactive app — couldn't be prerendered on the server." There's no reason it couldn't be, sure, but it's way harder when the clients are just as capable -- and, once things start getting busy, probably even more capable.