The fact that ignorant people might think they can make a judgment about someone's skill as a player based solely on gear score does not diminish the value of knowing the quality of someone's gear.
Gear score is that and ONLY that. A number that represents the quality of someone's gear.
It is useful in that no matter how much "Mad Skillz" a player thinks they have it will NEVER overcome a gear deficit.
on the other side of the coin however, a player who is jacked-up with the finest raiding gear available can still be someone who is unfamiliar with their class, fight mechanics, gemming, or an array of other aspects that will generally make them a less then desirable raid member.
that having been said it is unlikely that someone who has a very high gearscore relative to the current avg will be a bad player, although it does happen.
in summary, Gear cannot overcome a skill deficit and skill cannot overcome a gear deficit.
I would like to know the formula for wow-heroes and how it contrasts with other methods, like gearscore and inventoryonpar