People have this odd view that Flash had horrific performance, largely because their encounters with it as users were mostly with ads and graphics on the web that were terribly written and soaked up a lot of CPU. The same is true for tons of Javascript junk that pollutes the web now, but no one blames the language or the interpreter for that. AS3 ran inside a VM, so garbage collection wasn't linked to the browser's needs the way an embedded JS engine's would be (although it could take hints from the browser, as I recall). But the GC was excellent if code was properly written, and that meant a lot of good practices like ensuring weak references in event listeners and destroying / tearing down instances. You had to write code in a way that the GC would know to mark and sweep. Having said that, I tested a 500,000 line, single bullet Flash gaming site running on a beta version of the Flash plugin for iOS/Safari in 2012, on an iPhone 5, that was running particle systems and multiple game animations on screen with performance that would almost rival a javascript-based game now on phones that are 15 generations improved. If written well, and with a good understanding of how it managed memory, and keeping in mind what you had up on the GPU, from about 2012-2015 you could make the AS3 VM perform about as well or better than a reasonable graphics stack like PixiJS performs in 2026, on much lesser hardware. And you could definitely avoid memory leaks if you took care to.