If you got Gold then you know enough about your class and were able to do enough damage to successfully kill some things, and that means you're probably competent enough to dip into Flex/Normal.
The intent of Proving Grounds is not to wow or show your epic DPS for Heroic raiding guild recruitment, it's to help players learn new specs, and understand when they have achieved some competency to be a positively contributing member to a group of players.
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