The advantage of Flash was that is was a plugin that ran uniformly across browsers, and integrated directly into whatever hardware it ran on. The trouble with Canvas or even SVG is that you never quite know what you're going to get, and even today, they don't quite have the horsepower of what Flash was able to accomplish with vector graphics 15 years ago.

There are many things that i do not miss about Flash, and i do think it had to go due to becoming a security hole infested bloated mess and running terribly on smartphones; but boy do i miss that development GUI... and i loved Actionscript 2 and even 3, you know, when they worked...