Just because you only visit Hacker News it doesn’t mean that every website can do its job with an equivalent amount of JS.
The whole point of such APIs is to automatically provide the right content to people: Lightweight on slow connections, beautiful on the rest of them.
While I understand your frustration, I would certainly understand a web game loading more JS than, I dunno, some major text-oriented web sites where a similar page can be written with minimal or even no JS.
This I think is the point. The requirements are different, but to look at many web pages you'd not notice.
Too many resources that could be relatively simple pages with some code to aid user experience, are becoming massive full-blown applications pulling in megabytes of code and supporting assets.
Your game requires that code and those assets by its very nature. The vast majority of web pages/sites do not, and can probably be just as beautiful without (if not more so, as speed and responsiveness is part of aesthetic judgements).
You wouldn’t need such APIs if the developers didn’t shove so much baggage at the user. If the problem really is the result of competence then even the best APIs ever written won’t fix this.
I don't see this strategy being adopted by most websites, but I reckon it's a technique worth knowing about. I've worked on WebGL visualisations where the device RAM played a big role on performance for example.
What we need is ways to mark content as optional or offering it in multiple levels, that the navigator can pick from. This would be similar to how videos are served.
I also want to point out the Save-Data header which is a step in the right direction.