I actually said in the OP that teamwork stomps out a lot of these champs and that dealing with them isn't impossible if you have teamwork and coordination on your side.
So while it's worth mentioning, my point is that I think any champ that requires one specific strategy to counter, but goes squish when you use it, isn't a good design. I think the guys complaining about AD Sion for example, have a point, even if they don't know that they're making it.
The truly "bad design," in my opnion, is when there is no counterplay. Release Xin Zhao was a perfect example: he was going to ruin your **** no matter what you did. And Kassadin is dominion's example. Yes, there are things you can do to make him less overpowered, (buy MR, don't go into the jungle alone), but at the end of the day, whether that Kassadin does well rests almost entirely with the skill of that Kassadin: there is almost no counterplay that has any real effect.