Flex had some good ideas but many things made it a pretty bad experience to work with: Adobe abandoning WYSIWYG editing in Flash Builder, having two ways to do everything (XML and code) made things more confusing than it had to be, and the official components from Adobe generally weren't very good. I much prefer building by own in React.
AS3 was awesome for its time but TypeScript has surpassed it in my opinion.
After building up components directly in the language with React there's no way I could go back to using Flex.
I thought the message on Flash vs Flash Builder was a bit confusing.. but it came down to Flash being more for animation tasks, and Flash Builder more for building crud-like apps. There was overlap, but both targeted differing audiences.
I did find some object model inconsistencies annoying all the same, and some of the security implications in the early 00's frankly scared me. Even though I worked with it, I disabled it.
React + JS is nice, but the animation tooling in Flash itself was second to none. And still better than many options. If I still made a lot of elearning content, I'd be much more upset by the fall of flash.
Do you have WYSIWYG in React?
How much it will take you to implement from scratch in React an AdvancedDataGrid ?
I also like TS and React is my favorite way of rendering SPAs, unfortunately at my work we are stuck with JS,and angular1 so the fact that there may be nice things but are not built-in into html5/js is a huge issue.
Also how can I ask my boss or the other devs to start using X when next year X may be bad or outdated.
AS3 was awesome for its time but TypeScript has surpassed it in my opinion.
After building up components directly in the language with React there's no way I could go back to using Flex.