That said, for nearly every other aspect of developing thick client RIAs and complex visual experiences, flash/flex/as3 wins by a mile. From IDEs to the display api to as3 apis in general to the true object oriented architecture to lack of browser inconsistencies to client side storage to sockets and networking options to modular applications.
Say what you want about flash. It certainly has its problems and it has certainly been abused, but let's not ignore all the areas where js is still playing catch up and will be for a long time (even it's just IE). Flash has been a lead innovator in web-based interfaces for many years. Even if it's true that it's in decline, completely discounting such an important technology only shows ignorance.