Hell, I'd put the Winchester ahead of the AR too, honestly, for most of the same reasons. People really do care about their ARs, but they're in some ways just the flavor of the month. A 20-year RKBA heyday isn't really the longevity that I'd be looking for if I was looking for something to call the "national gun."
Flavor of two decades, by your admission. I see what you mean though. They're they new kid on the block compared with something like a Garand or a SAA. How about ownership rate per capita at a given point in history though? Surely that must count for something in the debate. Anyone know what the most popularly owned firearm per capita in the US ever is? Was the SAA more popular in its time than that Garand or the AR15? Not that this is the be all end all of the discussion. But I think its important. I'm too lazy to look that info up right now. And probably wouldn't know how to even if I had the motivation.