My personal opinion on katarina's ballance.

She is ballanced when it comes to numbers, her kit has the downsides that enemies can exploit which creates her opportunistic gameplay of big risk vs big reward.

But i see only one problem here, she is too fast. The time it takes for her to simply ... do her job is too short compared to the time it takes for executing her counterplay.

This means that katarina takes less risk, while still gaining as much as she was intended to.

People complain about and i feel them, katarina unloads her power at split seconds, while most of her counterplay was made so it takes time to deplay effectively, and katarina players know this ... they know when they can go in because enemies wont be able to react in time to stop them.

I wont go in-depth on the gameplay, because that always and i repeat always ends in one way, one side says that said champion abuses something that doesnt have an effective counterplay, while other side say that said counterlay is effective. This is a very subjective debate and everyone can see it diferently, my only argument is that katarina can challenge human reflexes, not to mention the delay on whatever can stop her.

Edit: After some time i noticed another thing that is indeed a problem, Katarinas design holds all of the possible interaction on katarinas side, Whatever counterplay she has cant be utilized until katarina makes herself vulnerable by her own decision, meaning that her counterplay is only effective when she fails to playe the champion