Ok, bois, this is like, my second post, ever, so I believe that alone should carry some weight, as I've been playing league consistently for almost 6 years. Here's my thesis statement: Most Tahm Kench players in draft and lower elos (50%-75% of players) use him (as far as i'm aware) as a support, and I think nerfing everything that made him a good support in hopes of balancing him in competitive play is a bad idea.
Allow me to explain. In season 9, riot has made 32 adjustments to Tahm Kench. 10 of those were buffs; the other 22 were nerfs. Let that sink in. Let's go over the biggest hindrances to Tahm Kench's support kit.
1: TK's q no longer applies a stack of acquired taste. Before, TK's biggest zoning ability came from landing a q on a squishy, forcing them to back up lest TK come and auto auto-reset for an easy w, and thus, and easy kill. Now, it's just a little bit of poke that slows, an ability that many other supports possess.
2: When TK eats an ally he is slowed by 95%. since TK isn't particularly fast, it's basically a root that lets you MAYBE dodge some skillshots. The only viable uses for it are snagging allies from over thin walls to escape a jungler, grabbing them from behind anivia and j4 walls, and removing longer duration cc, like Morg q.
3: E duration nerfed. Although it gives more hp, the only way TK could defensively help his adc was to eat them and run, popping e to avoid too much burst damage. Now that he's so slow when eating an ally, the 2 seconds runs out long before he can do anything with it.
4: R range nerfed early-mid game. This hinder's TK's roam greatly and makes moves on dragon and mid lane more difficult.
I'm not saying TK is bad. I think he's a little overpowered at the moment, actually. HOWEVER, tk doesn't really fit the support role very well anymore, especially with the reworks to support items last year.
This is just from my perspective. Please don't bash me in the comments. Instead, provide insight into why I may be right/wrong.