Tahm kench on release was advertised by riot as a solo laner that could function as a support..
The difference between then and now was that his playstyle was all about stalling the game by denying picks with W and waveclearing with R roams in order to deny splitpushes and scale.
Now he is a lane bully because for some reason riot wants him to be a solo laner again without putting his passive damage back onto his R and making him scale and fight to reach lvl 16.
Also taking away tahm`s stacking mechanic on q was the worst thing riot could have ever done, his q stacks were the only skill expression tahm had against mobile champs, meanwhile it didn't matter how strong his slows were, they were going to outrun him with dashes and blinks, all that slow buff did was make him oppressive against immobile champs.
So basically riot just made tahm more oppressive against immobile champs while making him useless against mobile champs, almost like they want this game to be about rock paper scissors...
Considering how long it takes for tahm to hard cc an enemy champ now unless you build hydra / attack speed on him (which in turn means you are going to do damage as him) Tahm can not exist as a champion that simply just detains enemies and doesn't kill them himself..
If he didn't gain damage from the attack speed / auto reset that he is almost forced to build in order to cc the enemy, he would basically just be a squishy single target pile of crap that occasionally stuns you if your teammates don't bodyblock.