When it came in though, Flash was a revelation in terms of what you could do with web design. Being able to have changing layouts that segued into each other, vector imagery and intricate little interactive animations really outclassed the very limited abilities of plain HTML at the time (which the implementation of HTML5 only caught up with many years later).
The introduction of Flash video was basically responsible for the creation of Youtube and its ilk.
I imagine a lot of today's game developers cut their teeth making Flash games too. (I did attempt
a thread about Flash game nostalgia a while back.)
So yeah, not needed anymore, but it definitely broke down a lot of boundaries for what you can do with websites.