The thing I hate about Katarina
...Is everything about her. Okay, I'm joking (I'm not) but there's one thing that stands out about her.
People say to deal with Katarina you just have to CC her. Okay, this applies to a LOT of squishy champs, although considering how Katarina is so reliant on her ultimate to succeed I guess it's fair enough.
But, CCing her doesn't work all that often. And it's because her rotation comes out_so damn fast._ Not her damage, but the speed she gets out her spells. It happens so fast that by the time you process she's there it may be too late to try to CC her, even if you have a CC heavy team.
Look at Scarra's pentakill there. How many of us can honestly say we could've reacted fast enough to stop that chain?
I seriously think that Katarina can get her rotation out faster than any other champ in League. Not saying she's OP right now, but adding in some actual cast times could go a long way to adding counterplay against her and mastery for playing as her. I wouldn't even mind Riot giving her compensation if that was the case.
Edit: After watching the clip, once Scarra cancels Death Lotus and starts jumping the enemies it takes literally about 2.5 seconds to mop them up.