Yeah, the Destroyer makes a bit more sense now. But I'm standing by my posts in 'ask the characters' because if the Destroyer drains Power, and Power is used for moves like Ember or Razor Leaf (moves that utilize sp attack), legendaries with higher attack or defense would win. "Everyone can Tackle", to quote Morphic. What I mean is, physical attacks would stay at full strength, because they consume no Power, and the Destroyer drains only Power. So, if I was, say, Groudon, and I was facing up against Mew, against whom I have no type advantage, I wouldn't start blasting fire at Mew, I'd crush her. My attack would be valuable to me in the War of the Legends than my Power.
There are three things wrong with this argument.
The first is that you're out of nowhere assuming that physical attacks in general don't use power. Every single official, capitalized move, except stuff like Splash and Struggle, uses power. Everyone can
tackle (as per the example of the Mystery Dungeon standard attack), but not everyone can
Tackle. For physical attacks, power is employed to exert more force on the opponent than physics would dictate for the given mass and momentum, hence why a tiny Nidoran Double Kicking a Snorlax can potentially do crazy damage if the Nidoran just happens to be high-leveled enough compared to the Snorlax.
The second problem is that during the War, the legendaries are
ridiculously powerful. Non-power-enhanced attacks are going to be laughable in comparison to even the most careless throw of actual power you can manage. Of course you're going to blast fire at Mew, or at least use your power for a Body Slam, instead of just pointlessly holding it all back.
Thirdly, and most glaringly, you're also making the unwarranted assumption that defense has nothing to do with power, when in fact it has everything to do with it. Pokémon have supernatural endurance, pain tolerance and recovery abilities, and that's all thanks to power. This means that by the time the War of the Legends comes along and the legendaries are all ridiculously powerful as noted before, Mew wouldn't even
feel Groudon stepping on it. Groudon would need to use power to stand a chance.