Why Nerf Kench Support? He's OP Top!
Tahm has a 51% win rate, but that's because that number is an aggregate of his win rate across all roles. Champion.gg shows his win rate in top lane is 53%...that's the role they should be targeting for a nerf...not his support role which has a modest 49% win rate.
That's why the nerf to Tahm's W on the PBE should be reverted. If anything Tahm needs a nerf to his solo laning capabilities, but to nerf his ability to save an ally (they are removing the speed boost he gets when running away) is hurting literally the weakest role of the 3 he can fill. It makes no sense, and to remove the speed boost completely is overkill. I can only assume that Riot is simply misinterpreting his win rate data and assuming he is a bit too strong in the support role, when in fact it's his power in top lane that should be curtailed.