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Well this is subject to change…

Not sure if we are talking from engineering point of view or from users' perspective.
Flash has great infrastructure and tooling which allows bad/non-developers creating things that still appear to work. Actually this is what end users experience as resource hogging. Like when the code redraws the complete UI every frame, even if it has not changed. Unfortunately this is trivial to do in Flash, and hard to do in JavaScript.
However the thing is that everything else is also hard to do in JavaScript (and its tool support), so complete imbeciles just have no chance to release arbitrary crap, because it likely will not work at all.
Retrospectively Apple may have acted right, but that time their browser was rather crippled from gaming perspective. They communicated that they would not support Flash, because they did not want to depend on Flash's development when allowing iOS developers to access device functionality. However at the same time they did not support WebGL until September, last year. There was no accelerated 3D in the browser until iOS8.
I think this is rather off-topic here, but it took time to write, so I just post it anyway :-)