You are right. I've done a lot of development in AIR myself and it is super impressive. Easy TypeScript like language. The Flex SDK is mature with all the standard stylable controls you need. Dedicated IDE that just works great. Easy deployment. I was able to build a cross platform (iOS/Android/Web/Desktop) video chat application with it and it looked and worked great everywhere. Someone dropped the ball somewhere with AIR.. I'm amazed they're still updating it.. that's something at least.
I guess it lives on here? https://github.com/apache/royale-asjs Still looks active..
Here's a demo https://royale.apache.org/tourdejewel