How is this a problem? Sure the tank never dies but at the same time, you aren't doing too much either.
I have ran into similar cases in Mundo and Mao as well. Want to know what we did against them? Ignored them. Full tanks do so little damage that you can literally ignore them even as a squishy. I was playing Lux at the time and I could literally ignore the Mundo hitting me for minutes at a time while I killed his friends and towers with ease.
Mao has some CC to be a bit more annoying, but can still basically be ignored as well.
Why is it a big deal anyways? It allows at least some on your team the ability to heal. That would be like saying ARAM is unfair since one team has a Soraka while the other has nothing at all since one side can heal.