I am going to tell you a "secret". A piece's power is determined by how many squares it can control.
In theory only. In practice, a piece's power is determined by how many squares it *does* control. No piece is worth more than the task it is fulfilling at the given moment in time. There are worthless Queens and game-winning pawns. There. I've just gone dogmatic. Meaning I'm just as bad as every one else in this thread :D
Reminds me of one of my favourite chess quotes:
"The Bishop is stronger, but the Knight is more cunning."
Anyhoo, we have different pieces good at different things under different sets of circumstances. The second you get dogmatic, you lose objectivity and may well miss the point entirely :P