Sooooo, Tahm Kench. Whats up with his damage?

I played a game yesterday against a team with a top lane Tahm Kench. Admittedly he got a little fed early on which likely led to him doing more than the usual amount of damage, but he build 100% tank/HP items and he could kill anyone on the team faster than their LB could, while simultaneously being crazy hard to kill.

I've never seen Tahm get that out of control before. Up until that point I've never really understood the complaints I see about him on here other than that his ability to save people is annoying. But when a character with 6 tank items can kill a target faster than an assassin it seems like there may be some slight issues there. He is pretty impossible to play against as a diving assassin anyway without adding in the fact that he can kill you almost instantly himself.

I've seen all the "you have to buy MR against Tahm" replys. Your right of course, you do have to. That's kind of a problem though. I should have to buy MR to protect myself from a fed AP carry, not a tank without a single AP item. I've never thought "wow, that Maokai, or shen is really fed. I should invest in some MR so they don't kill me instantly" Usually it goes "I should get some ArP or MrP so it might be possible to damage them later." Iif LeBlanc gets fed, you buy some MR to survive the burst and because she is squishy you can probably still find the damage to focus her down. Tahm Kench requiring both responses is a bit nuts.