The Thick Skin changes only hurt TK and went back on his identity
Before you downvote me because Tahm Kench is annoying to play against, hear me out. By the way, of course bias plays into this post, but who else to talk about why x champion is weak than someone who plays that champion?_ (Also, annoyingness does not currently contribute to efficiency, historically 'annoying' champions such as Teemo, Yasuo, and Quinn currently have very high numbers across the board)_
Currently the River King sits on a 47% winrate support with a 3% pick-rate and a 46% winrate top with a 0.9% pick rate (ouch). He sits at the bottom of each list, only topping Vlad (who's had his knees broken in and is 10x better mid anyways) and Ryze (a relatively recent rework with a high mastery curve, who is also much better mid) top; and Nunu, Annie and Lux support, who aren't even true supports in the first place. At no point in the game does his winrate break an even 50%, and players with 125+ games barely scratch a 46% winrate as well! :( Overall this makes him one of the worst champions statistically at the moment. [Note: Typically low winrates indicate one or more of four things: a) that the champion is hard to play, b) they are recently released, c) they are genuinely underpowered, and/or d) their counters are meta, thus making point c also true. I'll be the first to admit that while Tahm has some of the highest decision-making curves in the game, mechanically he's not all that difficult to play. His one-year anniversary has also already passed, and utility carries and carry top laners are meta right now, both of which counter him. This means that his counters are strong, he suffers from bad matchups (some of the worst top in the game, actually), and is not performing well AT ALL currently.]
In patch 6.13, a mini-rework of sorts rolled out for the River King that aimed to shift his damage to be more support whilst also heavily nerfing his Thick Skin ability. This is a clear indicator that Riot does not know, or at least has forgotten, what Tahm is about and how he is played.
When I play as support Tahm Kench, I don't give a fuck about damage. I want to be a tanky tank who can protect my ally and set up CC on an enemy. My Q already has good bases and my W chunks like nobody's business, but landing and utlizing both of those abilities on enemies requires an enormous amount of telegraphed set-up that allows the enemy to both peel for the target of Acquired Taste and punish Tahm for getting within range in order to chow down. Why did Riot force all of his damage behind landing three attacks when he can barely land one most of the time? Tahm is a bizarre character because he's a tank with no engage, no AoE cc, and more importantly, zero mobility. (Bringing up Abyssal Voyage to counter that statement would be like calling Sion mobile). The goal for support Kench is to both devour your ally from ganks and open up windows of opportunity to eat either of your opposing laners, preferably the ADC. Seeing as how Tahm bascially consolidates one champions into two when he devours his ADC, saving your CC until he eats the carry ensures a kill on both. Anyways, Pre-6.13 it was hard enough approaching and devouring a carry, even with Thick Skin. The ability is frustrating to play against, yes, but it is also his only defensive steroid on a slow, fat tank with no ways to reliably approach and catch up to carries, since Tongue Lash is blocked by minions. The point of the ability is not for 3-second, crappier scaling shields, but instead for extended windows in which Tahm can either waddle up to start a fight on the enemy duo, or waddle away from a gank. Currently the new Thick Skin punishes Tahm for doing exactly that, something that was clearly outlined as his identity from the beginning - Tahm is not a tank with high lockdown and engage threat. Tahm is a tank who exists as a meatwall between his carries and you. Tahm is a tank that provides nothing but shutting down singular picks whilst taking a serious beating. Tahm had a hard enough time approaching for a Devour without having his shield cut 30% in efficiency and 50% in duration. Nowadays, in a meta of huge AoE threat, that identity is already suffering, but also doubly so because Thick Skin feels so unsatisfying to use and completely betrays his gameplay and fantasy.
TL;DR the Tahm changes severely crippled his fantasy and gameplay mechanics. The changes only reward Tahm when he is literally within melee range on a ranged carry, which should never theoretically happen, and punish him for making the attempt to do so. He is already struggling in a meta filled with both high (dis)engage, and is no longer relevant in preventing picks because he will most likely not survive the attempt. He is countered heavily by most, if not all, carry top laners and is severely outscaled by tanks who can engage better than he can. I very much hope Riot considers looking into him, seeing as they have slowly been buffing weak champions the last couple of patches (Poppy, Lee, Thresh).
Sincerely,
A Concerned Tahm Kench main.