Six thousand years ago Rose Quarts led the Crystal Gems against Homeworld. According to the murals found in the episode --Serious Steven-- it depicts her even going against one of the leaders of Homerworld. Pink Diamond.
Judging so far that the hierarchy of Gems in Homeworld it is related to the rareness of the gems and assuming the hierarchy possesses some level of strength attributed to the rareness of gems, the Diamonds would be great leaders and great oppenets, due partially to the fact that diamonds in real life are nearly indestructable.
Pink Diamonds exsist, they are among the rarest gems in the world, most notably the Pink Star Diamond. If you look at the Crystal Gems you will notice on each of them there is some sort of star on their "Clothing". The triangle symbol that represents the diamonds also appears sideways in the middle of Steven's shield that he summons in newer episodes. So what if Rose Quarts isnt a Quarts but Pink Diamond herself?