No doubt Distant Cousin Bobby Lee would have done a bang up job had he accepted Lincoln's offer of Command of Union forces, however that is not to say Grant was a second-stringer.
The genius of Lee was how he managed to keep a war going when he was the far weaker of the two opposing forces. His innate knowledge of both tactics and strategy of mid-1800s warfare plus his knowing well the abilities, capabilities and weaknesses of his opposing numbers made the fear of 'What, oh God, what will Bobby Lee do!' a true terror in the hearts of Union commanders.
Grant took on Lee with the sure knowledge he had more troops, a continuing supply of them and an industrial base funneling more and more weapons and supplies opposed Lee dwindling number of men and material. He campaigned with constant, ruthless pressure on Lee as the most certain, quickest venue to defeat the Confederacy and win the war. As he said in a dispatch to Washington during the Battle of Spotsylvania Court House, "I propose to fight it out on this line, if it takes all summer." And he did. At Spotsylvania Court House, as he had at The Wilderness and future campaigns at Cold Harbor and Petersburg leading to Lee's surrender at Appomattox Court House.
Had Lee had the resources of Grant, he would have attacked the Union in the same relentless manner knowing full well that God is truly on the side with the biggest battalions and sure logistics. Lee would have aimed his superior number of troops and material directly at Washington D.C., taking it, bringing Maryland into the Confederacy and more or less ended the war on Southern terms.
Yes, this hypothetical on Lee is an opinion but it is an informed opinion backed up by some 50 year of reading on and studying the Civil War and I am not the only such amature or professional scholar to come to this conclusion.
Some folks on this thread may not like history, but what happened, happened and nothing short of a time machine can change it. To turn your back on what is past is to turn your back on what is to come. I pity the poor fools who do such for they have no useful future and all their senseless caterwauling adds nothing meaningful to the knowledge of man.
BTTT
Perhaps my use of the term “second stringer” was on the harsh side.
In terms of overall “talent” as a field commander, I believe that Lee holds the stronger hand.
I believe that given equal resources and manpower that Grant had, Lee could have truly preserved our Constitution.