To all those who say "if KF is so top tier then why is no one playing her?" Has it ever occurred to you that she is probably the least popular DC character in this game or people simply don't have an interest in her? I mean honestly that is one of the weakest arguments I've ever heard for someone not being good. That's like saying "if John petrucci is one of the best known guitarists, why doesn't everyone listen to his music?" Simply speaking, It's called preference.
Not everyone plays top tier like you do for the sake of playing top tier. Some people play the characters they consider their favorite comic book characters (like me with green lantern and sinestro. Started playing them day one because GL is my fave DC comic) or just play the characters with the most interesting game mechanics such as nightwing and WW with stance changes or how easy a character is to pick up and win with from the start with superman doomsday or batman. They could even pick a character based on the play styles they have in other games. A zoner from mk9 will probably be more interested in zoners in this game. It's a simple concept really...
In case that wasn't enough of a good reason. If I was a tourney player and already played green lantern and heard that killer frost was now regarded as better, I wouldn't switch to her. I'd have to learn new combos, new tech, new frame data, new matchups, new everything and then be comfortable enough to apply all these in a highly competitive setting in a relatively short amount of time. All of this for a character I don't even really like and then I'm expected to main her because she's better? I don't think so, man. Tier lists are speculation and theory just as much as they are based on results, especially early on in a games lifespan.
TL;DR: fuck you, read my shit.