Grant was something rare in that or any war. He could learn from experience.
I think making mistakes and discovering them for yourself is of great value, but to have someone else to point out your mistakes is a shortcut of the process.
I'm crazy about Grant: his character, his nature, his science in fighting and everything else. But I don't like the idea that he never accepted the blame for anything, always found someone else to blame for any mistake that was ever made, including blaming Prentiss for Shiloh.