Teemo just does Kennen's job better

Kennen has a range advantage but that isn't particularly meaningful when Teemo's blind can hit Kennen before his autos travel to their target. Comparatively Kennen has substantially less damage, delayed CC, delayed on-hit procs, and less tower taking prowess. I think the biggest issues can be highlighted by looking at where they hit power spikes and where they are strong in the lane.

Level 1: Teemo takes E, Kennen takes Q. Teemo wins every trade, denies CS. Kennen can.... uh, cs from a distance on one-three minions in a wave depending on minion retargetting rng

Level 2: Teemo takes Q, Kennen takes W. Teemo now has access to his farm-and-trade denying point-and-click cc. Kennen needs to expose himself to gain W stacks for the passive, then run through/passed the minion wave drawing aggro in order to even have a chance at landing his Q+W(p)+W trade and deal a grand total of 170 magic damage and 116 physical damage. Teemo meanwhile in the same trade can prevent all 116 of that physical damage and 10 magic damage while dishing out 3 autos worth for 168 physical damage and ~292 magic damage between 3 E's on-hit + ~6s of E poison + Q hit, which Kennen can not prevent when Teemo Q prevents Kennen's stun combo.

Level 3: Not much changes for either since kennen E telegraphs itself with the small hitbox and proximity requirement and temo W doesn't add to his damage

Level 4, 5: Teemo on-hit damage increases by 10 and poison damage increases by 6 per tick each level; Kennen Q damage increases by 40 each level, and cooldown decreases, letting him last hit with it against 3-4 minions consistently while Teemo gets free farm with his +30 on-hit damage on minions. Trading becomes more in Kennen's favor but becomes harder to do while Teemo's stronger wave pressure pushes repeatedly. Hope your JG ganks now or they won't be able to once Teemo hits 6.

Level 6: Teemo can't be ganked without sweeper, but Kennen has a chance to win a trade every two minutes with his ult, otherwise continues losing normal trades. Best chance is ifTeemo didn't start / and has no bonus health or resistances anywhere in his items so you can try to get a kill with an all-in R + . Also hope their JG hasn't decided to prey on the free lane opponent Teemo created turning your 2-minute cooldown into a 1-for-1

Level 7-10: Teemo scales through these levels harder than Kennen as Teemo's on-hit damage reaches 50 + 30/tick and his Q click increases by 45 each rank while Kennen's lower AP ratios and lower per-rank Q scaling coinside with weaker per-rank scaling of W damage as well. Worth noting Teemo reaches these levels about 2 ahead of Kennen both taking optimal trades.

Level 11+: Laning phase will be over around this point, so Kennen can finally contribute to the game with ult in team fights while Teemo is level 13 and storming top's inhibitor uncontested.

I thought this was just me at first, but checking the matchup in every elo it seems to show the same story -- Kennen can get a kill with ult+ but otherwise gets hard pressured out of lane and doesn't have the ability to contest the stronger split from the champion that does his job as a ranged harass lane bully better than he ever could dream to.

Kennen of course loses to other ranged champions besides Teemo, but at the very least they don't do so by just doing Kennen's job better.