Sure you can probably balance your power. But even if you got both legs balanced to put out the same amount of power in the same places during the pedal stroke, the bike is still moving in surges of power. And concentrating on strengthening one leg is just failing to also increase the power in the other leg, so you wind up with a balanced but less powerful engine.
I suppose if your legs are way way out of whack it makes sense to strengthen one to a reasonable semblance of the other.