To be entirely honest, I think Tahm could use a nerf

Damage scaling off of tank stats is always a bad idea. For the most part, the champs that have it are fine, like Voli. Tahm, is fairly different, though. His q is a very versatile skill. It's good for poking, chasing, hard cc'ing, and does a crapload of damage. His w is arguably the best peel in the game, while also boasting a damage equal to 1/3 of the targets hp. His e is actually the skill I think is alright, since tho it gives him 2 hp bars, you can play around it...usually. His ult passive is insane, though the atcive is semi-weak.

The fact he can build full tank and tower dive basically anyone at level 9 just seems unfair and is frustrating. I would recommend buffing ult active, but nerfing the passive, lowering q damage and/or slow duration, and/or lowering w damage.