That's the argument American officers made during Vietnam, killing ten Vietnamese for every American. Thing is, the American people don't care about the ten, they just care about the one. I don't consider the Overland Campaign one of Grant's greatest successes (it's stiff competition there). He fought Lee mostly after his best subordinates were killed or wounded. Lee had to personally command the army (half the size of Grant's), the cavalry, and I Corps after Stuart and Longstreet were shot, but every time Grant tried to maneuver around Lee's flank, Lee got there first and entrenched. At the North Anna, the army was divided and vulnerable, but with Longstreet wounded, Stuart and Jackson dead, Hill sick, and Ewell suffering a mental breakdown, and Lee himself ill, the opportunity to inflict a defeat in detail eluded him. Grant spent 60,000 men getting to where McClellan started two years ago, and didn't understand the evolution of entrenchments in the Eastern Theater. He considered an entrenched army half beaten already, since that had been his experience in the west, when in the east it served as an economy of force measure, leading to bloodbaths like Cold Harbor and the first assaults at Petersburg. In an election year, this sort of casualty intensive method is perhaps inappropriate.
I don't really hold the Overland campaign as a whole against Grant's technical skill; he wanted to land in North Carolina and launch a long range raid against the railways there, but Lincoln vetoed that plan. Lee held possession of the capital until after a hypothetical Democrat president would have taken office, and only failed after having prolonged the war for three years, after both the other key Confederate armies (Mississippi and Tennessee) were destroyed. I think Lee played the poor hand he was dealt extremely well; Grant also played his hand well, but I think if anyone got to pick between what the two were dealt, they would take Grant's hand.
I think it's possible to imagine an 1864 campaign in which Lee keeps the Union on the north side of the Rappahannock, depending on how last year's campaign shakes out and on his best subordinates not getting shot. That in and of itself isn't enough to win the war, but it does give the Confederacy some breathing room. If he drives them from the field, he can maintain a force to observe the Rappahannock while sending reinforcements to the Army of Tennessee, and let expired enlistments eat up the demoralized Army of the Potomac.