"Muh Kata bad early and cc her"
Many people actually think that
has a bad early which is completely false.
Ofcourse, she cant kill you instantly in laning phase like
but in exchange she gets the safest farming skill in the game.
Her q is excellent in farming and poking, and she can stay in safe distance. It will also hit every melee champ she plays against. Also she gets even more easy farming with her w. The next thing is that she has a flash on a 10 sec cd. Enemy jungler ganking you? Just ward+e and you`re safe.
Since you can poke the enemy laner down to like 30% health you can also all-in him and finish him with ignite.
"Muh cc her if she jumps in and she is dead" Many people think that she will be useless if you cancel her ult, but this is totally wrong. Remember her passive? If her team gets her a kill she can just jump on you with her q, w and e (which actually deal some dmg) and kill you.
Also dont forget that she can buy Zhonyas, which means that she can do the following: Jump in -> Ult for 1 sec -> Zhonyas -> get reset from team -> clean up
This champ is just way to rewarding as a assasine.
Also for the people who think that she is only good in low elo, i want to mention the 90% banrate in Korea.
tl;dr Riot should balance Katarina so her Banrate doesnt reach 90% in other regions or she will end like the old Kassadin.