[camus]

doesnt matter , they use it under the hood. and the fact that you have little control over how ExtJs actually uses the DOM will not make your app faster...

[as_if]

That's a two-edged sword.

If I rely on an API, which abstracts everything, I benefit of every performance improvements they make "under the hood".

If they are better with performance than me, I win. If I'm better with performance than them, I lose.