The proprietary tools were only an issue for people who needed the timeline. Games-wise, Both Actionscript 2 and 3 were perfectly usable without Flash. The MTASC compiler was a massive game-changer, and then Adobe released the AS3 compiler themselves, and certainly when I was at a consultancy working on a massive, expensive game, none of us were authoring anything in Flash. Even the designers and artists simply provided image assets.
A few years later, I did use Flash to teach students interactivity (in 2016, I was wondering why myself, but hey, university courses are hardly up-to-date) but there was little other reason to use it.
Today, I still rate AS3 and if there was an LLVM project to output, I don't know, WASM, or similar, I'd try it. Oh, there are?
- https://github.com/bvibber/wasm2swf
Of course, MTASC wunderkind Nicolas Cannasse went off to create https://haxe.org/, which was used quite well on Smart TVs and the like for a while, still used in games. Maybe we already have the answer, but the web is too boring for this stuff.