At the point that Jobs wrote his lie filled "Thoughts on Flash" Flash Player was vastly more performant at HTML5y things like animations, video and music playing than doing it in the browser.

I'm not going to defend the quality of the flashplayer architecture and implementation (due to it's crapness) but it was perfectly fine performance wise - it was a 'resource hog' because of the terrible, terrible code that people wrote for punch the monkey flash apps.