Actually in terms of bandwidth JavaScript isn’t the problem, you can fit an entire SPA into the bandwidth required for one large image (it is a problem in terms of CPU usage on underpowered devices though)
Large images being “worth the trade off” is debatable depending on your connection speed, I think (though at least you can disable images in the browser?)
Some browsers used to have "click to show image" too. I know dillo did. Actually, come to think of it, its browsers that have really dropped the ball on helping out users with slow connections.
Now they are 1200x750 high resolution JPGs, but that is a worth while tradeof when we have screens that can display them.
The real issue is Javascript.