You don't want to use "Plot Protection" to explain what happened? Fine. Lets say that SeeD were more powerful than her. That make them more powerful than a being that was "eating" the entire universe. That means they are damm powerful. Much more than Kuja, or Kefka, the other villains(with exception of Ex-Death) or heros of the other games.

Some people here, try to use the argument "she was defeated by SeeD" to prove she was weak. But this argument doesn't work. She was absorbing all existence and gaining power from it, proving that she was much more powerful than the heros(because they cannot do something so impressive like that). But if she was much more powerful than them, why she lost? Exist only two logical explanations. Or she did something wrong(didn't kill them when she could, for some reason), or SeeD gained a great power boost and beated her. In one way or another, she still was absorbing the entire universe. She still was doing something more impressive(and that required more power) than any other FF villain ever did.

And that scan don't contradict anything stated in the game.

All this discussion is ridiculous, really. I could ask to a child of 10 years old(maybe less) "Who is more powerful, a guy that can destroy a planet, or a guy that can destroy/absorb the universe?" and her/his answer would make more sense than yours.