How does this even make sense?

I know that the grades given are based off of how you play a champion and how others play a champion, but when you go 23/6/16 as Nasus and get an A+, not an S or even an S- and the Blitzcrank on your team goes 12/13/20 and gets an S- I start to wonder a couple things. One if you are one of the players carrying your team, and everyone else on your team has at least double your deaths how does having 4 less assists make up for 11 more kills. Is Nasus just that broken that you need to go 25/0 to even get an S-, and loads of people see that Nasus is broken so they do stupid damage builds where he can easily 1v5. If that's the case(I'm gonna hate myself for saying this) Nasus should get a massive nerf. I could 1v3 no problem with a pitiful 350 stacks at 30 minutes. I like the idea that Nasus in theory can never stop doing more damage, but if you get good CS early game, you can even be outplayed with 40% CD for an almost perma-slow, enemy armour reduction, and an insane amount of damage. I feel as though you should get better grades if it seems you hard carry your team, and also that Nasus and other OP characters should get a nerf. Thanks for reading this :P.