Having spent some time developing a Flash-based application with a framework I fail to remember (which included forms, database views and other stuff), I know w

Having spent some time developing a Flash-based application with a framework I fail to remember (which included forms, database views and other stuff), I know what you are hinting here. However, the difference is stark: the Flash-based UI was horrible. There was no excuse for it, except the alternative would have been Internet Explorer and ActiveX-based components. There was no Chrome, and JavaScript was horrible in every regard except if you happened to know a hipster framework called jQuery. The choice was between bad and worse. Flutter (and probably other mobile UI frameworks) provide a choice between good and great (which of it is the native framework is a matter of perspective). Product managers and developers could decide to go with native widgets, but they decide not to, and mostly because good UX is being delivered by these custom frameworks too. That would be a low bar to cross, but for many, they provide a lot of productivity boost as well.