Popularity doesn't necessarily equate to greatness, or higher quality than something less popular.
Atlanta brought up a great point about bands standing the test of time. I think, in order to consider a band great, it should be generational in its scope.
Aerosmith, CSN&Y, Doors, etc. are all examples of generational music. I'm not sure you can say that about the Eagles.
I remember going to see Aerosmith for their Permanent Vacation tour, and all the kids waiting in line, talking about what a great new band it was. Lol.