Actually, the Civil War general with the highest casualty rate among his men was ... Robert E. Lee.
The claims about Grant being a butcher are based on his “fighting on this line if it takes all summer” of 1864. When you are facing an enemy, you can go around his right, around his left, or attack head-on.
Getting around the enemy’s flank usually requires you outsmart him. Outsmarting Lee was pretty difficult, but Grant tried repeatedly to get around Lee’s right flank. (He didn’t try the left flank because that would take him away from his base on the sea.)
He succeeded at Petersburg but was done in by overly cautious subordinates who didn’t follow up their successes.
Grant was the opposite of the Union generals who got hit hard then retreated back to base for a few months. When Grant got hit, he just shifted a little and tried again.
Think about what might have happened in the Seven Days had Grant been in command. He would have counter-attacked not just retreated. Quite possibly Richmond would have fallen.
Same for Chancellorsville. He got hit just about as hard as Hooker did in about the same location. (The Wilderness.)
Grant didn’t retreat, he just shifted left and tried again.
Thank you for that information.