It is definitely decentralized. How decentralized is debatable, but there is definitely enough above-ground gold spread around in enough hands to consider it decentralized.

Gold's problem is portability. This is why paper gold became a thing in the first place. It is far more convenient to trade IOUs for gold than to trade the actual asset. Yet, no one will see this as a problem so long as most aren't trying to turn in their IOUs for the real thing.