These decks are not overpowered. They probably lose more against aggro than they win (albeit with a small margin). I just don't like people being able to just draft all value cards regardless of color and have no real problem with their mana base.
The problem I had with the vivid's is that they seemed to facilitate 4cc or 5cc a lot. As in a three color control deck that splashed a card or three from the other two colors just because it could.
My C/Ube on Cube Cobra
My C/Ube on Cube Cobra