Incidentally, last I checked, no replacement for the marquee tag, either. That tag had a lot of features, in fact, and when I looked a couple years back there seemed to be zero projects that could actually replace it completely. A bunch of things that used to be very easy to accomplish, using that tag, now aren't. (now, maybe none of those things should ever be done, I suppose, so perhaps it doesn't matter)
Mobile first was the issue. Adobe bought it and blundered about, they could still resurrect the thing but have no vision.
Linux and Windows. Yes, it ate power like it was free.
Taking that into consideration, Flash worked pretty damn well on Android. It wasn't doomed because of its mobile inefficiency. It was doomed because both Apple and Android knew that they could never convince developers to build for their 30% tax walled gardens if Flash remained a fee-free alternative on the open web.