Scoring system adjustment

I think you guys need to make an adjustment to the grading system (S, A, B, C, D). Implement a time scale as well, so if the opposing team surrenders at 20 mins, you can still have a hopeful chance of achieving a grade S. As of right now i've yet to see someone achieve a S grading when the opposing team (or my team) surrenders. It is unjust to have someone who was fed and doing a great job, then the opposing team surrenders and still only gets A. Thoughts?