End Game Rating

Last game i played was a 37:23 min lenght.

I was playing ADC and ended up losing with a score of 10/4/6 172 CS for a total of 13.375 gold. IMO this is pretty good considering that the average KDA/CS of my team was 4.25/8.25/9 and 119.75 CS.

I ended up getting a end game rating of B+...

On top of that to make matters worse i had the most total damage done to champion 31.423 AND total damage dealt 146.112 of my team!

I even got 1 of the 3 tower we manage to get down...

I mean i know i lost but ffs! i did all that and i only got an B+?

Comparing it now to a previous game i played not long ago.

I was top lane we ended up winning in a 24:43 min lenght. Ended up 4/2/4 159 CS total of 9.299 gold. Total dmg to champ 8.114/ total dmg done 77.953 and 1 inhib down by me.

I get an S+...

Where is the logic in that?! Can someone explain to me?