Champion scores should compare you to your team
I don't know if it does already, but I have carried many feeding teams and still got scores like A-.
If your whole team is doing very well and you're 7/0/10 it's not a big deal. Your whole team is fed, and you're fed. I mean, it's still good to be 7/0/10, but all you had to do was be in teamfights to get 10 assists, win lane to get 7 kills. Your enemies might be 0/5, 1/3, 2/7, etc. The hard part is just not dying.
But if your team is sucking and you're 7/0/10 it means a lot of things. You're able to not die against the fed enemy 8/3 Tristana. You won your lane, but you were also able to assist your feeding team and help them feed less. You're doing well against fed 10/5 enemies rather than 0/5 enemies. You're holding your own when your team can't.