Canvas is a last resort if you absolutely cannot build the thing any other way.

When you use canvas you're giving up on not just accessibility but also optimizations that the browser does for you transparently when you use the native render tree. There's no guarantee that your app will be faster in canvas, it could easily be slower. Do you really think you can beat the browser's C++ by writing code in a language that doesn't even have a native integer type? Perhaps you can, but your base assumption should be that you can't.