As someone that has worked around and with flash for years, I say good riddance. Though there are portions of the flash 'product' I think are much stronger than HTML5 and javascript (specifically, I feel that actionscript 3 is lightyears ahead of javascript), Flex was always one of the weaker parts. It always came off as half baked and did not blend well with everything else. The whole concept of MXML files was ridiculously obtuse and only led to unmaintainable code.
My only disagreement is with your disdain for MXML. AS makes it a lot nicer to build UIs than, say, Java with Swing et al., but I still prefer some sort of structured language like XML or even S-expressions to build a UI with over the procedural "make new widget, set the attributes, add it to this other widget" pattern.
I did some work with flex/mxml stuff about a year and a half ago, and frankly, it ranks as the worst software development environment I have had the displeasure to use. This includes the 8086 chip with 1 LED for debugging.
As another Flash veteran I completely agree with this. If you ever look at the Flex source code it's so obvious that it has been hilariously overengineered (which probably explains why Flex apps have always run so poorly).
I don't think Flex ever really had a suitable target audience - the premise was being able to create cross-platform/cross-browser widget applications, but that was hindered by the fact that the entire app ran on the AVM (with all of the limitations that entailed).
Anyone that wanted to deliver a great user experience (or had performance constraints to consider) would end up writing a native app anyway.
