> In 2002, there were 665 million internet users, now there are 3.4 billion and growing
A significant part of that 3.4 billion are on mobile, which is even deeper prone to the overused JS problem.
> terrible standards implementations
Ah, you mean IE6. In it's prime time, it was a brilliant browser, standards or not; it was a necessary evil to forcefully move things ahead. It has XHR, webfonts, a gazillion things none of the browsers had yet. It indeed stuck around for too long, but this was not the case in it's initial state.
> lack of processing power
https://hackernoon.com/10-things-i-learned-making-the-fastes... -> Read the paragraph "#2 Do mobile first. Like, really do it."
We do lack processing power on mobile, so for that 2-3billion people, who are using mobile _only_ or mobile first, we need economical solutions.
> why not take advantage of the device requesting the service?
Because you can't assume the device is powerful enough to do so.
Why do you think https://mbasic.facebook.com still exists?
> Set aside the 5 second delay user experience annoyance
You go against one of the initial hard rules of the web with that. I wonder if is the importance of speed had changed, but judging by the grouchy voices all around, it did not. People only keep using the services because they deliberately made it hard to leave or because they learned tactics from Microsoft and are constantly eliminating competitors.
> and realize that as a business there is no way to scale your services profitably without offloading as much work as possible to the web client.
Now, this is complete nonsense; there is no money you save there. How is generating all those React apps, shuffling all that data is better then generating HTML? :)
Of course, there are exceptions, there are always exceptions, but most of the things would not need mammoth sized invisible JSONs to be parsed in the browser while the pre-rendered HTML could be served and manipulated only when needed.