Flash, specifically Flex, won the battle and then promptly lost the war as other companies remade the internet in Flex's image.

Adobe's sudden and not at all inevitable betrayal of Flex devs was a huge shock and absolutely killed Adobe in the field of Rich Internet Apps which at that point they were dominating.

If they'd pivoted Flex to compile to Javascript then the world as we know it would be a very different place, one where we would have been happily producing web apps in MXML markup for the last decade rather than recently rediscovering it through the medium of React and JSX.