Wtf is happening with grading on league...... i played vayne once and went 19,6,10 and got an a and in the same game a lucian that was 9,4,3 got an S WTF and a 17,4,11 morgana got s- but i got an A wtf pls sort this out riot
They have. You need to do your research. The grading system grades your performance on an individual champion in that role (since a Top lane Vayne will perform differently than even a Bot Lane Vayne).
That would mean that it is useless to try to compare your performance as a Vayne against the performance of a Lucian since they are different champions.
They do this because champions perform vastly different from other champions. Some get high kills. Some get low kills. Some get high CS. Some get low CS. I assume you get the point.
It would be entirely illogical to grade a Janna's performance the same exact way as you would a Vayne.
It's because KDA isn't what wins games, it's everything you do that contributes to taking down the Nexus. Kills, damage, healing, CS, objectives, vision etc. are all things that might impact your score. If you are too low in one area it'll drag your score down.
6 deaths is too many deaths. It also has to do with your cs probably, but your op.gg hasn't updated so not sure.
It takes MANY things into consideration.
These are just some things we believe it takes into figuring what you receive: KDA, CS, objectives you helped take, wards (placed/destroyed).
KDA is not the be all end alldecider of your grade. Champion popularity can have serious effects on this grading scale as well since it compares you to other players of that champion & role combination.
I think it's really stupid how CS is the large factor in your grading score. You could have amazing score, kill participation, take multiple towers and even be the main factor for your teams win but if you don't have super great pro level CS then you won't get an S...Hell...you can go very negative in score like 3/6 but have super high CS and you'll get an S..
Some what an example, though maybe not as extreme as I mentioned but:
I just had a game playing ADC 
and went 13/2/14, I had the largest kill participation at 71%, took 2 towers, did the 3rd highest damage in the game, put down and destroyed the most wards on our team. The only thing that was bad was my CS which was 208 since I got zoned out a lot in the early game due to support 
. Just because my CS wasn't super good I only got an A...
Then my friend which was playing Jungle 
who was doing poorly this game due to counter jungling 
. He ends up going 2/7/12 with 109 CS, with only 37% kill participation, took no towers, did the least amount of damage on the team, and placed/destroyed the lowest amount of wards and he still got an A as well.
I just think the mastery system is stupid that it mostly focuses on how many defenseless minions you can kill rather than how much you really did for your team in taking towers. or securing/placing vision or having a high kill participation.
