> I don't see why one computer (or one small group of computers) should be responsible for doing work that could easily be performed in a more distributed way by people's browsers, if only because it's cheaper to offload that work onto the client and leaves less ways to crash the server-side application.
Of course, this has always already been the case! That's why we don't stream our webpages as images (or video, if you need to scroll), but instead offload the work of rendering a graphical representation of the symbolic HTML representation to the client-side browser.
It's a pretty solid idea (apart from the Browser Wars), and one of the ideas that made the WWW viable.
The ridiculous part, however, is where people somehow decide that we should wrap more and more and yet another layer of abstraction onto it.
It's not that web servers have grown less powerful and therefore need to offload more work onto their clients. The demands on web servers are higher today, but they've also grown more powerful, and we came up with some pretty clever scaling technologies to deal with those higher demands. But offloading code execution in the form of client-side JS is not really one of those, in practice.
Yes, the idea could technically be used to accomplish that and make less work on the server side, but really, take a look at this page, or any (bloated) page like the problem we're describing; That's not what's going on here, it's about the same amount of work on the server side, nothing's being offloaded, just more work on the client side.
At least the Flash-only-interface websites that plagued the web 10 years ago offered us UI elements that weren't possible in HTML back then (for better or worse), but today's JS bloat truly doesn't add anything that can't be done in a much leaner, less client resource-intensive way.
Even your spreadsheet example. Sure, run the calculations client-side, that only makes sense, no need to throw out JS with the bathwater. But what sort of calculations are we talking about, realistically? For a medium spreadsheet, a few hundreds of summations and multiplications. Nothing of the kind that should make a 5-year old computer even blink. But whatever these types of apps are actually doing they manage to crawl the jankscroll already even on an empty document, let alone when you try to use it.