Why is Tahm Kench allowed to exist as a full tank that outputs more damage than most carries?

The first Devourer Tahm Kench that I saw in the jungle literally built devourer and full tank. He had 25 kills or so and 20k higher damage than the next person in the game? WITH FULL TANK. I started getting really pissed that Devourer Kench was a thing, but now, I am even more pissed because support Kench can still do the same thing WITHOUT DEVOURER. 2x this week now I have gone against a support Kench that built full tank and no one could kill him. Or get away from him. Or duel him. Or kill anyone else around him for that matter. Its annoying when the only counter play to Kench is to all in his carry when he engages, switch to him as he is running away with said carry in his mouth in an attempt to cc his fast moving ass, and then go after his carry again as they come out of his mouth, and then finally if you have anything up attack tahm kench again.

His slow needs to be shorter duration, his devour needs to have way less base dmg, and it also needs to have a much longer cd. I literally watched a zed last game get demolished by support kench and a shen get eaten 3 times by him in an attempt to escape him which did not happen mind you. In fact once he slows you, you HAVE to flash away from him in order not to get eaten. Dude, seriously, I'm done with this game until this champ gets fixed. I've seen a few OP things this season, in fact, Graves comes to mind, but even tho he's scary as shit, you can still kill him relatively easily for that damage he has. The same is not true for the Kench man.