I somewhat agree that his top role is worse than his support role. In the current meta he's really good as a support dealing a fair amount of damage, and having a fair amount of tankiness. The main problem is that almost all players don't go tahm top anymore because he's expected to build health in order to deal more damage. Instead most players go Ap or full Crit tahm kench. These builds actually deal more damage than just building health and the damage scales into late game really well. Another major reason people don't go full hp tahm is that his damage scales extremely low late game. So even if you build him with Sunfire Cape, Iceborn Gauntlet,Frozen Mallet hes not going to deal alot of damage late game. No matter how fed you are early game, you are outscaled by most toplaners and midlaners damage. You just become a useless "toplaner support" by only being able to CC your enemies(which is really hard because you need 3 stacks of your passive to stun and you get kited too easily by many champs) and save your allies with your "w".
What doesn't make sense even more is that Riot decided to nerf most of the tank items health. As well as that, sunfire capes damage was lowered. This was 
main damage item because you would be able to devour an enemy for up to 6 seconds.
What riot said a few years ago "Many moons ago, Tahm Kench was a monster in the bot lane. Impossible to kill yet also dealing massive damage thanks to the passive on his R, the catfish/frog/demon thing was an abomination to champion diversity and basic biology. Early this season, nerfs to his Q, combined with changes to the greater ecosystem overall resulted in The Benching of The Kench. Since then, Tahm’s nerfs have proved to be too effective. In his current state Tahm Kench is both unplayed and depressingly weak. But how do we buff Tahm without dealing with the same problems he had before?
We're taking a direct shot at a part of what makes Tahm so frustrating to face, his pseudo-invincibility. Tankiness is always going to be a part of The River King, but it was a bit insane for a support to take on both members of the opposing bot lane without a care in the world. Instead, we're moving some of Tahm's power from defense to offense with the help of a changed passive. In addition, Abyssal Voyage will now get ol’ Two-Coats where he needs to go much more effectively. These buffs should more than compensate for Tahm Kench's reduced tankiness without making facing him such a rage-inducing task"
Now they decide to nerf his offensive items and release him as a free champion to play for a week. They moved his power from defense to offense but then moved it again from offense to defense. My point: his passive is now ridiculous and even more useless. Why bother to build health items to synergize with the passive if i could build others items that don't synergize with the passive and are more effective to him? Part of his kit that used to be on his passive is now wasted.
My suggestions: Just remove the health passive. It is considerably weak and un-noticable. I'd rather play tahm kench without that extra passive that's not helpfull.
