I'm not going to comment on the YT aspect of it, but I still think there's extra value for Flash itself as a technology, particularly that it's vector-based (also, interactivity to a lower extent) whereas video is bloated by comparison.
I know a lot of people don't like it, though I still have the standalone player on my computer (not Windows). There is also Ruffle, which might work fine for animations (personally: the loading time isn't great, also lack of zoom option).
I mean I know this probably depends on a platform more than anything. But there is the Internet archive.
Albuquerque: THE MOVIE EDIT: Better yet, Everything You Know is Wrong by the same creator