In many situations Hitler was presented with the info but either chose to ignore it or was shouted down. However I dont buy the Assertions that are some of the German Generals memoirs that they knew what was best but were held back by the rantings of a raving lunatic. There is a pattern to the memoirs, take credit for the successes and blame Hitler for the failures.

Manstein may have been a good Commander in Chief East but I'm not so sure he would have changed the course of the war. But if any German Commander was to take charge then Manstein was probably the ablest.