Arbitrary code execution is a vulnerability where you write and execute arbitrary code outside of the intended environment
Just because Actionscript is a language doesn’t mean it has the functionality to do whatever to your machine. It lacks most of those functions because it is mostly a graphics library. It would have to run an already prepared external script via some improper memory pointer somewhere for it to be arbitrary code execution.
And Actionscript is not built on top of JavaScript. Both JavaScript and ActionScript are based on ecmascript. They are different, just like Typescript and JavaScript are different.
Actionscript was object oriented and had proper types unlike JavaScript which to this day is one of the worst programming languages.
Are you sure I’m the one misunderstanding the problem of evercookie? Was the problem that you could access the same cookies from multiple browsers because of ActionScript, or was it that evercookie maliciously restored said deleted cookies after they were supposed to no longer be used? One is a feature that allows transferring sessions between browsers on the same computer. The other is essentially malware.