To me the main difference between the generalship of Grant and Lee was in their armies.
The ANV was custom built and officered to Lees specifications for the kind of war he was going to prosecute. The AoP was built to the specifications of McClellan to fight the kind of war he wanted to fight.
As in most wars the CW was determined by which side could impose their will on the other, on how their war would be bought. In Va. Little Mac failed to impose his will on Lee and thus his army was improperly trained led to effectively fight Lee on his own terms.
Grant found that political and military realities of 1864 precluded the necessary retraining and reorganization that he AoP needed. Fortunately the quality of the fighting men in the ranks of the two armies was not nearly as unequal as their leadership, i.e., Grant was able to essentially make up for the deficiencies of his senior officers and other inadequacies of the Army as long as the Army itself remained sound.
Grant most likely could never had won within the constraints of May to July 1864. But after that then US finally closed one of the two remaining blockade runners' ports. That allowed the US fleet to re-deploy to only blockade Wilmington and Charleston and then prepare for the attempt to end the blockade entirely by closing all the ports.
Then Grant severed the most direct and best RR leading into Petersberg, and Sherman severed the last remaining RR connection between Atlanta and the rest of Georgia and Alabama.
Once that happened Early had to try to remain in the Shenandoah valley to protect the harvest. He was unable to do that.
Therefore Lee's defense of Richmond/Petersberg, like A.S. Johnston's counter attack at Shiloh Church, caused huge casualties and degraded Grant's standing, but the cost was large. Mobile Bay was not adequately garrisoned, the counterattack against Warren's corp on the Weldon RR did not have weight to it to expel the US forces.
Hood was temporarily left blind in Atlanta. Not one part of Sherman's army, but all three groups made it to the Macon RR and Hood's divisions barely escaped.
Which all set the stage for Winchester III. The Confederates probably out fought the US forces at the tactical level and it did not matter.
Sheridan had a cavalry force that was going outflank the Confederates no matter what they did.
Lee was protected by Richmond and the Confederate Government. Everyone else had to pay the price for General Lee's success.