Lets address tahm kench
Tahm Kench currently has 2nd lowest win-rate in normals (44.7%) 4th lowest win-rate in bronze (45.0%) 2nd lowest win-rate in silver (44.4%) 2nd lowest win-rate in gold (43.7%) 3rd lowest win-rate in plat (44.5%) 5th lowest win-rate in diamond (44.6%) (i cant find stats for him in Master+) And overall 2nd lowest win-rate in ranked (44.5%)
The above win rates were used from LOLKing In Champion.gg he has a win rate of (46.04%)
Now, i know that some champions will always have to be at the bottom but the fact that tahm kench has consistent low win rates in pretty much all elo's + normals shows that he is seriously struggling.
(The average win rate from bronze-diamond is 44.4% if you do the math)
Now i know that on release he was a pretty annoying champ to go up against. And riot decided to give him some nerfs but i think that the stats above show that he needs some buffs or some nerfs reverted to bring him up to speed again.
I have some suggestions that could improve his win-rates but keep in mind that i don't work on the balance team so don't take my suggestions to heart.
(Speed up the animation of his ult) I think we can all agree that it takes forever for tahm kench to actually use his ult. The animation takes pretty long even if he instantly activates it and the enemy team gets a huge and long lasting indicator that tells the enemy he is on his way. Its pretty much a worse version of twisted fates ult except that he can take a buddy with him.
(Give him movement speed when carrying a team mate AWAY from enemies) I find it pretty weird that he only gets a movement speed bonus if he is carrying a team mate towards an enemy instead of away. I, and many others, usually only use his W to run away and save your adc instead of going towards them (If you're support).
I don't have many more suggestions besides maybe some stat changes. Let me know what you think!