Flash was not slow, it's just that flash ads were ahead of their time in abusing the system's resources. The supposed slowness of flash relative to browser api's was a myth, although flash content was bloated, in much the same way that modern web pages are bloated. When flash was killed by Jobs I knew it was just a matter of time until people did the same bad things with JavaScript and CSS as they did with flash, and lo it came to pass.
As much as I didn't like installing Adobe's plugin, I have to defend Flash. JavaScript is just recently getting to the speed Flash had years ago. Flash probably still does vector animations better [citation unavailable].