There's a reason she's banned in 99% of the every ranked game i've ever played...that should tell you something riot, and that something isn't good. No champ should be able to completely decimate entire teams like she can, nerf her ult already and free up a ban spot so that it can be used for others. She's a nightmare for 1v1 and teamfights.
90% Banrate in Korea I wonder if she will beat Kassadin`s old banrate of 95%
She might be on the road to it.
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There's a reason she's banned in 99% of the every ranked game i've ever played
Let's see. According to Lolking, she's banned just under 35% of the time. Hyperbole isn't helping your argument.
No champ should be able to completely decimate entire teams like she can
She only decimates you if you clump together and don't focus her. Literally all you need to do to shut her down is silence her mid-ultimate.
nerf her ult already and free up a ban spot so that it can be used for others
If you're honestly banning Katarina, you're probably in bronze.
She's a nightmare for 1v1 and teamfights.
Not only is she easy to shut down in her ultimate, she's even easier to shut down in lane. Literally pick any champion that pushes the lane 
and Kat can't initiate without getting stomped.
tl;dr, you're just salty because a Kat beat you in game. Riot's got bigger problems champion wise that they have to worry about right now: 
They already nerfed Katrina. She was a Category 5 in the Gulf but hit land as a Category 3.
