I feel like you can do pretty much everything with HTML5 and JavaScript that you could with Flash and ActionScript. The IDE for Flash had some nice UI abstractions but there's no reason that couldn't happen in a web IDE in 2019.
Distributing your website like a flash file/app as a binary is one missing feature I suppose?
As consumers, most people probably only care about what modern browsers can do. As a developer, the mechanisms become front and center. Modern web development is a Rube Goldberg kluge of things glued together with duct tape. Flash was much more coherent and imposed less cognitive burden of tying it altogether.
Not just NPM - the "web" is a diverse set of APIs with various peculiarities. It's not inviting to an artist with little to no programming experience (and even with the potential to learn). That was the advantage/disadvantage of flash - closed system, one (major) IDE, one language/standard library.
I'd need to see some performance metrics to come to that conclusion. "Bloated Flash site loading with a progress indicator for a few seconds" was pretty common and a huge complaint about Flash and its use on the web.