I can see where you're coming from, but I'm not sure that I agree with it. Every champion has their own particular strengths and weaknesses. Yes, some are more obvious than others (don't try to 1v1 Fiora or Jax. Save some CC for Katarina's ult. Buy a QSS when laning against AP Malzahar), but there's almost always some counter-play involved. So Sion and Tryndamere are terrors at low elo, but rarely seen in high level play. This is because the counterplay there is fairly obvious, and most players past a certain point can deal with them. So yes, that leads to certain champs being more or less common at high and low elos, respectively, but I actually think that this is good design. After all, they purposefully make the lower-IP cost champions easier to play, but many (not all--see Ryze) have lower rewards for mastery. Compare Annie to Brand, and Yi to Fiora, for examples.

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.

What about raid boss players?

Ya. a well played Kassadin just makes me want to quit. he always get kills + never die

How do I check this?

this one time, i killed a yorick and a jax at the same time, and i got an achievement for it.

I hope you realize you made Mike rage quit and then troll us with Sejuani for the entire night because of the nonstop Lulu bans.