Nothing wrong with Flash and Silverlight except each being controlled by a single company. I liked those technologies. Adobe Flex was very nice to program in and use for it's time.
Games were made in flash so it can't be that slow.
Maybe slow for time to load. I think we got that down a bit and this wasn't to render content but a utility for a signed up user.
Modern day SPAs are far, far worse offenders when it comes to smothering resources.
I was so happy when it finally started to disappear. That kind of sheer disregard for my system resources is inexcusable.
As for the speed of the flash player itself it was quite good.