IMO there’s still nothing that’s quite as good as Flash. Efficient vector animations that perform consistently across all major browsers are still unusually hard for non-developers. There are some solutions, but they usually aren’t as designer or animator-friendly and require a huge JavaScript library to be loaded. The barrier to entry for non-developers (or inexperienced developers) creating games that run well cross-browser is still quite high too.
I remember creating a Flash-based chat system back in the day. Before WebSockets and Server Sent Events, Flash was the only way to get bidirectional sockets in a web browser, other than Java applets of course (which were pretty locked down by that point).
Ruffle is obviously as good as Flash, by emulating Flash - but yeah, the creative environment is missing. We need some .io page that clones the old way of churning out 2D games and animations.
We’re in a stupid period of computing where a legitimate way to get games on smartphones and computers is to publish software for DOS because everything has some kind of emulator for that archaic platform.