Not true, apparently. Gordon Rhea, author of four books on the Spring of 1864 campaign, has studied the battle at Cold Harbor in great detail. His detailed study of the Union casualty lists has reduced the Union casualty count to between 3500 and 4000 dead for the morning charges, and a total of 6,000 casualties for the day. Compare that to Lee's almost 10,000 casualties at Antietam, roughly the same number from Pickett's Charge, 5300 at Malvern's Hill, and it's clear that the butcher in this picture was ol' Marse Robert.
Well, by your reckoning, since 58,000 men were lost at Antietam, then the Union lost 48,000?
Better check your figures. I am afraid Lee wouldn't be the butcher in that case.
And...Grant wasn't the General at Antietam (Sharpsburg), so a comparison is not correct. By that score, i could throw in fredricksburg....