I still largely blame Adobe here -- they were the ones who should have been responsible for fixing Flash's performance. The complaints about it being a CPU hog

I still largely blame Adobe here -- they were the ones who should have been responsible for fixing Flash's performance. The complaints about it being a CPU hog weren't limited to mobile; even in the early 2000s, Mac users, at least, generally hated being forced to deal with Flash-based UIs. Adobe never seemed real concerned with optimization, I suspect precisely because of the advantages you listed, e.g., things that were hard-to-impossible to do without Flash. At this point, at least, I'm pretty sure WebGL can do most or all of what you could do in Flash. It's possible that the tools have never caught up, but it also seems possible to me that the space that used to be occupied by Flash games has largely been filled, ironically, by mobile gaming.