I couldn't believe my eyes when I saw these changes first show up on Surrender@20.
This isn't just a nerf to Tahm Kench in the top lane, it's straight utter removal. It's murder. For one, it's a straight damage nerf. His Q doesn't apply his passive anymore, which also doesn't stack, meaning that his first auto attack technically deals more damage I guess but everything he does after that is completely worse. You want to know the kicker? There's one thing the PBE doesn't mention - not only has his Q's damage been completely neutered, it doesn't apply a passive stack anymore! Tahm Kench has to land 3 auto attacks as a fat, enormous, immobile hitbox in order to use his empowered spells. I was flabbergasted when I first hopped into the PBE and was landing Q's to see that they didn't add a passive stack. It was an alien experience. Imagine playing Braum and your Q doesn't apply Concussive Blows, or if Kai'sa W didn't apply Plasma. It's a totally unnecessary nerf that comes across as cruel and vindictive. Chasing, already difficult vs mobile targets, is now 10,000x harder when you've lost a primary means of applying stacks. Not only that, you've lost probably 2/3s of your damage in any sort of 1 on 1 scenario with the double passive/Q nerf. Add in the removal of enemy Devour's utility just for shits and giggles and you have what amounts to not just a nerf, but an overly harsh and rather vitriolic removal of a champion from a lane.
Where am I supposed to play this champion? Pro play has completely destroyed him. Ally Devour is a ghost of its formal self. It's reached the point where the only use of is pre-emptively devouring before predictable skillshots. The crippling slow and grounding mechanic you introduced earlier in June makes it often a detriment to you AND the person you ate when you're being ganked or in the middle of a teamfight. It's still powerful enough in coordinated play, yeah, but absolute trash 9 times out of 10 in Solo Queue. Support Tahm Kench feels like an uphill chore, and it isn't fun at all anymore.
The only solace was that you buffed solo lane Kench (which historically was hot dogshit). Now that's gone. Is Tahm Kench annoying to play against? Yes. He is. But he also falls off like a rock past laning phase once his target selection loses its potency and struggles in a lot of matchups, like versus GP and other Juggernauts. I don't even mind a nerf! He's shot up in popularity especially in high elo and he does have some unhealthy play patterns in how you're supposed to deal with him.
I think that the right way to nerf solo Kench is to definitely address his oppressive Q slow, which these changes did by reverting the buff. I also think that removing the mana restore on enemy Devour could be good by emphasizing how powerful it is no matter who you eat. Lowering his base and scaling health all do wonders to reduce his early power and even a little bit of his damage without completely gutting his ability to fight lane opponents. The E changes are whatever, I've grown used to Riot just throwing shit in the air with regards to that spell just to see how it lands. Less shield, more sustain seems a fine tradeoff, although it really really really hurts later in the game to have a worse shield less often. Tahm Kench is _supposed_ to be tanky, and over the years Riot has just repeatedly nerfed his main source of tankiness time after time.
Overall these changes seem not only excessively harsh but just....unnecessary? You're straight up removing a champion from a lane when common consensus seems that Tahm Kench is healthier for both Solo Queue and pro play as a solo laner provided he has clearer weaknesses in laning phase. Riot, I beg of you to not force these through to live and shelve them as you have for the Wukong and Teemo changes. I hate the way this new Tahm Kench feels and plays and all that you are doing is removing the ability to play him in a solo lane, which is destructive and unfair, especially considering how many times you have repeatedly gutted support Kench. Nerf him, yes, but please stop removing mechanics from his kit and please do not completely neuter his damage.