Costume Gears: Usable or Unusable in GVG areas?

[hachigatsu30]

Could always do the lesser known thing called "learning by doing." You fail to kill a certain player, you assume they have something under their sleeves, you try a different strategy. You fail again, you assume they have something else, you try another. I still call it a challenge...
Plus, there are some people who can't stop themselves from bragging about what they have lol

Also, MVPs are scripted. Players aren't. If an MVP is scripted to cast random status ailments at random times, maybe that certain MVP isn't meant to be killed by someone without Ring of GM Powers. Also, if the gears are equally good, there are certain classes that overpower other classes, and there are classes that overpower those certain classes (feel the grammatical correctness in this). Same goes for class builds.

What I get from your WoE explanations though, you're saying that even with costumes available people are still gonna rush in with all different classes with all different skills to confuse the defender? Then why disable costumes?