I haven't seen it all put together into something that's really web friendly though.
I mean, the product was already Adobe Animate for years at that point — a tool for animators, not IxD developers; where the intended export product is a video raw to be fed into AfterEffects, and any ActionScript support only existed to do things like character rigging automation, mouth-flap sequencing, etc. In other words, for replay-time (⇒ render-time) computation, not for interaction.
The Animate runtime had essentially, at that point, evolved out of being a software runtime per se, and had become something rather more like a custom demoscene "demo" runtime — an abstract machine tuned for compactly representing instructions to procedurally generate a video+audio stream when executed. Something more closely related to mod-tracker abstract machines than to a thing like the JVM.
I'm not surprised that everyone else left; the product for IxD folks ceased to exist in 2016, when it was renamed. That it still kind of worked if you did this or that was a coincidence, not intentional.
I am surprised that the animators themselves then left. What made them leave? The whole product still works just fine (if not better) for their use-case.
That's ... terrifying.
I’ve worked in Adobe air based infotainment systems 10 years back, and it was a great technology. Actionscript3/MXML was at that time far more advanced than JavaScript. It took maybe another 5 years and typescript and react to catch up.
The graphics primitives the web provides are actually not that great at emulating Flash's specific graphics model. SVG and canvas differ from Flash in a few key areas, especially to do with masking; and WebGL/WebGPU are very low-level and rendering vectors on GPU is hell.
This could have been fixed by having Animate switch to an SVG+SMIL renderer for HTML5 projects, but Adobe wanted a quick fix to keep Animate relevant beyond Flash Player.
Adobe's official answer to Flash on HTML5 was "rewrite your AS3 app in CreateJS and use Animate's HTML5 exporter to export your timeline as a series of bitmap spritesheets". This is not at all what Flash developers needed, but Adobe is a terrible steward of their own platforms, so its what they did.
As a result it forced a lot of Adobe's own customers to jump ship for greener pastures. The game developers jumped to Unity, the web developers to Lottie and GSAP, and the animators to Toon Boom.