Project Mayhem
Experienced
I think you've got some grammatic errors here.
The word "outstanding" literally means "to stand out", there is nothing constraining that to a singular element. Oxford dictionary defines it as "exceptionally good".
The word "greatest" is a measure and as @TG3K says, that has to be measured by a metric... And with art, there is no absolute metric (this is the same to me as "best").
You could say greatest based on album sales, or concert revenue, or largest catalog of songs, etc. Anything that is not actually measurable can not by definition be used to assign the label of "greatest" except subjectively.
No errors.
Correct, greatest is a measure, and in the absence of a specific metric (as in this case), and in this context, I would default to impact on music and culture. And yes, we could debate what constitutes "impact" . But let me put it to you this way, has there ever been a band that had a larger impact on music and culture than the Beatles? Who was bigger (measure) than the Beatles? The only thing even close is Elvis, but he's obviously not a band.
Better yet, would any member of any band listed in this thread claim that they are greater than the Beatles? (man I hope Alcatrazz or Oasis wasn't mentioned)