Kennen really needs his kit updated to 2019
His kit is a relic from 2010 and hasn't been updated to stay relevant with all of the mobility and damage that has been added to the game, on top of itemization changes. It's awkward and has poor synergy, compared to the kits of other champions with similar team fighting function.
Back when he was released, his kit was great. His E gave him the mobility he needed to get good ults off and damage was much lower, with team fights being much more drawn out, which facilitated his sustained damage. Now, with all the mobility and damage that have creeped into the game, his E no longer provides sufficient mobility, and his damage is spread out over too much time, which is a problem when most other champions can burst you down in 1-2 seconds.
It does a poor job of enabling him to succeed at his team fighting role and forces him to rush specific items (Protobelt + Hourglass) to cover its' weakness, which completely removes any build flexibility.
In order for him to be useful, he needs ~20 minutes of AFK farm to complete the required core items. This is one of the reasons you sometimes see him in pro play, though rarely: most games are played safely and he gets to farm top lane for half an hour with little to no interaction, and then joins his team with his core items and an additional AP item, which he does poor damage without. In solo queue, however, the game is usually largely over before or around the time he builds Hourglass, and he doesn't make it to a third item.
You can look at his win rate vs. game duration and see that there's a pretty clear problem:
https://i.imgur.com/Znz8xrp.jpg[]
https://i.imgur.com/vxafx4B.jpg[]
His win rate is the highest in games that end early, meaning that he didn't actually do anything and got carried by the rest of his team winning their lanes early. It drops once it reaches the point where he's able to team fight. He normally doesn't get Hourglass until around 20 minutes.
Compare this to a champion like Vladimir, who has a weaker early game, but functions similarly: farm until two items, and then become a team fighting powerhouse. The difference is that Vladimir's win rate increases as he completes his core items, while Kennen's doesn't, because his kit doesn't allow him to fulfill his role effectively.
https://i.imgur.com/kPDMr3K.jpg[]
Basically, Kennen wins games not because he fulfills his role as a strong team fighter, but because he's an incredibly safe champion who can't bring his team down. He doesn't help his team, but he also doesn't hurt them. His impact can only be neutral or slightly positive, but it's very minimal when it is positive. He essentially allows his team to easily carry him.
He really needs to have his kit brought up to date with 2019, ideally by taking away some of his safety/early game power, and modifying his kit so that he can actually perform his team fighting function without needing to rush two specific items, and then still not doing any damage until the third item. Most games don't last long enough for him to get to his third item, and his power with that third item isn't proportional to how long it took for him to ramp up.
A quick and easy fix would be to rework his E to either be a more reliable gap closer or an actual defensive ability. Given that he has to dive into the enemy team, the 10 armor and magic resist does nothing to keep him alive. It's his only form of defense and mobility, but it's tied up in movement speed, so it's completely shut down by snares, slows, disengages, and any form of CC, and gives plenty of reaction time to his opponents. Also, the movement speed it gives is misleading, because it pushes him over the cap even without boots.
> But I'm a Gold IV player and ranged cancer always stomps me!
The only exception to this is at low MMR, where he can actually win the lane, because unskilled players or players who don't have knowledge of how to play the match up do the standard 'oh no ranged cancer top is hitting me, I am doomed' panic and try to run away when he harasses them, instead of trading.
Champions like Jax, Darius, Riven, etc. can dumpster 50% or more of his health if he gets in range to auto-attack them post-6, because their engage range is longer than his auto range. The only champions that have trouble against Kennen are ones that can't touch him, like Singed and Garen, but they're not commonly picked.