Zero won like 40+ tournaments. He can probably play against us with one hand strapped to his back and he will win. using him as an example when hes is the undisputed best Smash player is full of ****.
I admit to not know which costumes are exactly op since I didn't use them myself. But aren't Donkey Kong's Kong Cyclone and Pikachu's Skull Bash generally considered too hard to deal with? I mean, I did a little research a while ago and this
http://gfycat.com/DefensivePhonyCaterpillar didnt look like something fun to deal with.
And about the notion that if a costume is OP it should be banned, I am sorry, but if you ban ONE THING trust me that all the gates of hell will break loose. And how do you definitely decide that something is OP anyway and convince everyone of it? generally there will always be people skilled enough to deal with any kind of **** you throw at them and there will be whiny piss babies who will want anything that they cant deal with ever banned. It will be a huge never ending cycle of mindless debate and there will always be the "Thats OP and needs to be banned!" people and the "Its not you just need to learn to play against it" people. I dont want that headache. You have no real goal that can be achieved. Just because Palutena and some other characters have costumes that will get them up in the ranking doesn't mean we should get ourselves into that endless sea of debates and hatred. Especially not when the existence of costumes in tournaments will just bring many characters who have **** costumes down further into the tier lists. basically defeating this imaginary goal costume supporters have in mind.