i think the greatest thing we lost with flash is even non-technical people making something in an editor, hitting export, and getting a single small file that worked similarly enough to an image that it was trivial to just upload somewhere and have it be embedded there.
This. I hated flash sites, but it gave non-technical people a chance to be creative. Designers especially loved it, though they often used it for wrong purposes (web pages) too.
But good luck teaching them how to make that tetris clone in React nowadays...
