Grant and Lee commanded armies for about the same amount of time - Grant actually commanded for several months longer. Yet it was Lee's Army of Northern Virginia which suffered the greater total casualties in raw numbers than armies commanded by Grant. So if Grant was a butcher then was Lee a greater one?
It is the head to head Grant-Lee Overland Campaign I refer to whereupon Grant (as a butcher) simply drove his men in a battle of attrition at Lee - regardless of casualties - knowing Lee could ill afford major losses. Grant had almost twice the casualties of Lee at the Wilderness and Spotsylvania... and (basis some reports) 7,000 casualties in twenty minutes at Cold Harbor.