Are End Game Rankings Broken?

So it was later in the night, and I had decided to do one last game of the night. I thought to myself, "I'll play top, maybe some urgot, yea, I feel like eating people." So I lock in Urgot and see that they lock in a Yi top. My duo buddy tells me to play a bit safer because he is m7 urgot, and I'm m6, and that he's played against a couple Yi tops before, and that he out damages me early. I started off strong, with a gank from the enemy graves I get first blood from the Yi, AND get away alive. The game progresses and I begin to do amazing. I roam to lanes, and get some more kills, I keep up on cs, I have good vision along the map, and no other lanes have hard fed their lanes. I help with a couple towers, and objectives, and by the end of the 22:31 minute game, I am 10/0/5. First perfect game in quite a while. My vision score was 19, second only to the support at 22, had the most damage dealt at 18661, and had 127 cs, once again, third only to the enemy ashe at 132, and our adc jinx, at 149. A. Fucking. Plus. Normally I wouldn't be too mad about getting a good game and no S or S+ for a mastery 7 token, but my score was nearly perfect. The only thing I could have possibly done better was more cs. But as a top laner, with decent clear, and not some instant wave wipe ability like anivia (of which my duo buddy was actually playing) I would assume that nearly 130 cs at 20 minutes would be S worthy. I GUESS I THOUGHT WRONG. Rito what the actual fuck. I get I'm just a low elo insignificant player, who does the minimum 10 games of ranked at the very end of each season to get placement, and a player who only plays for FUN and not competitively. But my score was nearly perfect for not being a fucking challenger. Where is my mastery 7 token.

[sg-shisa]

The thing that really gets me, is that it wasn't even an S-, but an A+. At this rate mastery 7 on Urgot, and most likely some other specific champions is literally impossible.