And yet, there's still no good replacement for building those types of Flash games. HTML5 game development isn't close.
Technically, yes. Commercially, no.
Unity is just one example that can export to web. There's https://playcanvas.com/ too and a plethora of other stuff :)
Unity demo: https://wasm.bootcss.com/demo/Tanks/
It'd be a great open source project. As a commercial product, it'd probably be enough to support a small team, but I don't see a way for it to get huge.