No one has ever said that Kennen can't instakill you. Whoever said that is either a complete moron or was coaching a Mundo.
As for the rest of your post, no.
In that clip, Kennen was able to burst down 3 very squishy targets, as well as finishing off an already low Olaf.
He didn't just have "proto+zhonya".
Get your facts straight, he had
.
If your champion can't do something well with that many items, that champion is just bad.
As for "The best laning phase ever", that's complete and utter bullshit; His only real strength early game is his (rather mediocre) range.
By the way, ranged tops are not OP.
If that were true, we would see a hell of a lot more

If you are a bruiser/fighter/tank (as most toplaners are), you just have to survive under your tower for 6 minutes until you can pick up
, at which point he poses no threat to you.
Hell, if you are someone like
, you don't even need to wait. Kennen is so goddamn squishy that he won't be able to deal with YOU. Oh are you NOT one of those 3? Don't worry, on the off chance your jungler comes to your lane pre-6, Kennen will likely be put in a Flash or Die scenario. Unless you get the gank at a bad time, and he has his W passive up, he can't stun both of you.
In mid, he is even worse; his range advantage is completely nullified against most opponents, and his only way of pushing the wave is either slow (autos) or extremely dangerous (E+W the wave). Not only that, but if gets matched up against someone like
, he is completely fucked. People like her can force Kennen out of lane or kill him extremely easily, and oh boy...
If Kennen wins lane, he is a menace. If he survives lane, he is a factor. If he loses lane, however, he is one of the most useless sacks of shit you have ever seen.
Without damage, all he brings to the table is a 1.25 second stun (not even immediate). Hell, he is so squishy that he might not even get to do that before he gets hit by a primordial burst.
Oh, and you can't say that Kennen can go untargetable just because Zhonyas is a core item. By that logic,
and the like are sources of true sight, since they all buy 
And by the way, none of this is new. Kennen has been doing this same shit since he was released. He is better at it than he has been recently, thanks to the mage update, but he still isn't as strong as when Zhonyas Ring was here, and his current power level is hardly exceptional. People are just calling him OP because he is getting picked for once and they don't know how to deal with him.
Here is the clip, by the way
https://youtu.be/69j-uGa6xkM
I guess
is cancer OP too, then?
https://youtu.be/4K86231HAcE