How I see it is perhaps flash was ahead of its time (back then), most peoples bandwidth struggled to load flash content quickly enough, I think if flash had arrived now (but without the existence of html5) things might have been different.
Regarding the security issues, well I think long before flash was marked for death people (folks influential in web standards) started to disregard it, so less and less effort and time was put into patching security issues. I am sure its the same with any other medium, they all suffer security issues but are eventually patched sufficiently due to continued development and confidence of filling a web standard.
Also can you name one webtool that is non-coder friendly that exists today that can take full advantage of the power of html5/css in the same extensive way flash did?
I am sure some will come, but I think its a bit slow in coming. I have used some tools such as Macaw (discontinued now

) which enabled "decent" designing of web content, but was a far cry away from what flash (the software) could do in the hands of an artist. Ok sure flash has its action script but even without using that (or very minimal) an artist could produce something great.
I realize websites these days are far more complicated in context to function and back-end stuff, clients demand so much more such as social integration, dynamic content, responsive layouts/light weight..etc etc and HTML 5/css are doing a fantastic job of that, but I feel flash was never given the opportunity to try integrate itself into modernizing web standards because of the hate for it so early on in its evolution.
Also I am not saying that websites are boring these days, there are many many awesome designs out there, but the more exotic designs that an artist could have otherwise have done in flash (or something like it) are now solely in the realm of experienced web coders.
Just goes to show how important some knowledge of code is these days for an artist to apply his or her trade in areas of digital interactive mediums.
I knew flash was pretty much dead for a long while now, yet I am still sad to see it go and sad to hear adobe announce its final nail for its coffin.
I had many wonderful years with flash, so long!
King of the impossible!