Well, with Flash they were also beholden to Adobe to fix bugs and optimize it for whatever GPU they wanted to use. I'm not sure it does take 5x as much process

Well, with Flash they were also beholden to Adobe to fix bugs and optimize it for whatever GPU they wanted to use. I'm not sure it does take 5x as much processing power, especially when you can ship things off to the GPU. You have to remember that these decisions were made a few years ago, and Adobe Flash video on mobile (where available) has always lacked the performance of native apps/HTML5 video.