I call a bit of BS about this. In the end, the code that creates js or HTML5 equivalent (poorer versions in fact) end up being far more resource intensive and buggy than flash was. Importantly, this is after millions of man hours were put into optimising the hell out of the js engines. Further, apple itself ended up optimising it's processor architecture to allow faster JS execution.
What would have happened if Steve Jobs hadn't made an ultimatum on Flash? The iPhone might have taken a few more iterations, but eventually they would have figured out how to support flash well in their phones. We might even be in a place where processors are designed to efficiently execute flash (the new M1 has so many specialization this is not even reaching out).
Instead what we have today is a mess of things that still don't add up to technology we had a decade back, and we have really bad, inefficient code running everywhere trying their best to emulate what flash did.
In the end, the reality is that Jobs made a tech forecasting mistake assuming HTML5 (not js) will eventually catch up with flash. It never did. As poor forecasting decisions go this is fairly reasonable, but we cannot move forward if we continue insisting that this was the best decision even in retrospect.