Champion Mastery is so damn broken

I got a score of 1/0/20 on lulu support and I got an A. Omg an A like really? This game I was watching my position carefully so I dont get myself killed (its not easy getting 0 death). I was buffing my allies making sure they get out of the situation alive and buffing them to help them get kills. I put down wards, help destroy turrets and killed a dragon. But the other team decides to surrender preventing me from getting more assist. Which I find this unfair because I have no control over that to get the qualify number of assists to get to S. Its so broken because it is pretty much based on luck.
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