Sure, a device can still be wildly successful even if its missing something important, but that doesn't magically make it a good idea at the time it was done.
The replacements for flash suffered from poor performance for a long time.
Flash still suffers from poor performance to this day, let alone back then, and even on full desktop devices (hell, it'll turn on a Mac Pro's fans). Flash on phones was a miserable idea to start with.
I was basing my opinion off of my personal experiences. For years after IOS devices hit the market, flash dominated certain types of content on the web. The lack of flash support meant that a user couldn't really view these sites on an IOS device.
Also, in spite of flash's performance issues, for a long time it seemed to perform better than HTML5-based video players. Youtube's HTML5 player remained an opt-in experimental feature for so long for a reason, it simply didn't work as well as the normal player.
Floppy drives. CD drives. Ethernet ports. Flash support.