[egypturnash]

Actionscript 1: a simple little language that could only be entered via a huge dropdown menu

Actionscript 2: basically Javascript, when I was writing stuff in AS2 my O'Riley pocket JS guide saw a lot more use than the pocket AS guide.

Actionscript 3: completely ECMAScript4, Macromedia/Adobe was on the standards board for that, but then Mozilla went a different way, I think, it is a giant mess [1]. Also AS3 was a lot more verbose than AS2 which did not endear it to the people with one foot in art and one in programming that was a large part of Flash's user base.

1: https://auth0.com/blog/the-real-story-behind-es4/

[wslh]

In conjuntion with AS Flash offered animation capabilities that were impossible at the time. This animations are from 2000: http://swain.webframe.org/zeek.html

[bdefore]

As your source indicates, it was Microsoft that stonewalled ES4. By the time Adobe agreed to let it die, it was a capitulation that they had been vetoed.