> The modern web bloat has just been due to huge amounts of JavaScript becoming common - if you compared basic video playback it was normally at least a factor of two worse playing the same video in Flash
Well, sure, for simple video playback html5 is clearly superior. What I find more interesting though were flash's "interactive" capabilities—if you wanted to make an app that ran in the browser, it used to be you'd almost always use Flash. Now you just use tons of Javascript instead, and I think if anything that was a performance regression.
If you don't use a huge toolkit, a modern browser is massively faster – I last did benchmarks like 8 years ago and even then it was usually an integer multiple more memory or CPU for something done in Flash versus the browser and that was before accounting for the browser having better quality text rendering, color management, alpha effects, antialiasing, etc. Had Adobe not just stopped investing after they hit 90% marketshare that might have been different but they were sitting still for too long.
The problem is that having made things like JS, the DOM, CSS, etc. so efficient just increased the threshold before performance forces developers to notice inefficiencies but that's a pretty portable problem, too — we had to force Flash developers to test on older systems with slower connections the same way.
Well, sure, for simple video playback html5 is clearly superior. What I find more interesting though were flash's "interactive" capabilities—if you wanted to make an app that ran in the browser, it used to be you'd almost always use Flash. Now you just use tons of Javascript instead, and I think if anything that was a performance regression.