We've all been thru games when we feel a teammate deserved a S rating...

... for carrying the game but he merely got an abysmal rating. That is a flaw with the system. Judge us on the game itself, not some imaginary comparison with some other imaginary player who happened to play the same champion on the same role in other games. And makes all other teammates and opponents in my current game irrelevant. In its current iteration, it wouldn't matter at all if the rating system is shown to us in a chart somewhere else. Because we're compared to some other imaginary average person... Fix the ratings system, have better understanding on the parameters fixed or just junk the system. It is even more terrible that a reward system such as Hextech crafting is attached to it.

Just look at Overwatch's Play of the Match system- That is something thoroughly relevant to the current game the player just played. Even when it's not accurate all the time, it's a good system.