Ashley, just a small Point. People without background knowledge may misinterpret your message.
I definitly agree that the cpu is likely much slower on mobile than on desktop. So is javascript. Nevertheless webgl is very fast on mobile too. Just to give an idea it is possible to render a lvel of quake3 at 60fps on ipad2. It is what i means by very fast.
blog.tojicode.com/2010/08/rendering-quake-3-maps-with-webgl-demo.html
It is impossible to do so on canvas2d. To render 3d on canvas2d Is possible. but it is slow and produce an visual of poor quality compared to what webgl can get.