Think of it like this...
Power tells you it's "relative" strength when compared to other characters.
But team synergy and game mechanics is like a game of rock-paper-scissors. "Rock" teams might be good defensive teams that can withstand offensive output like crazy, while slowly dishing out damage... easily winning against "Scissor" teams. "Scissor" teams might be teams that rely on Special attacks and their use of stuns/potency/etc... which can't defeat the tenacity driven "rock" teams but can easily defeat "Paper" teams. "Paper" teams are TM driven and high offensive output and can simply destroy whatever defenses "rock" teams have, but are prone to stuns, dazes, and other special attacks.
Is the power level of the "rock" team indicative of its strength if it goes up against a "paper" team of equal power? Or what about a "scissor" team?