The North had the correct strategic outlook of the war from day 1 with the Anaconda plan. They quickly apprehended that the South needed outside provisions in order to fight the war, and that the US Navy had substantial advantages over the confederates.
The south had amazing tactical leadership. What they lacked was Winfield Scott and his overall strategic outlook to start the war. Lincoln knew how crucial the Mississippi was to the overall plans of the south.
Basically, the overall strategy of the North was to force the South into fewer and fewer options and force them into making poor decisions.
However, it must be said. If it were Lee and not McLellan, the war would have ended in ‘61. We’d not be talking about the war between the states today if it had. The union had the correct strategic outlook, they had the men and the materiel, they just did not have the command to pursue and destroy the enemy. They did not have to.
I'm going to throw on my best David Tennant and say....well, I don't think the war would have ended in 61, but Lee was definitely a far superior general to the like of McClellan.
However, I think it is important to point out that Lee was not the perfect general either. (Here we go and I will get ready to duck).
He had an overdeveloped sense of the offensive. While this did serve him in that it provided him with more than one tactical victory, it put him in some pretty tenuous situations when the Civil War devolved (yes opinionated verb), into positional warfare. It put him at a strategic disadvantage and made him slow to adopt the entrenchment and the positional tactics that would eventually rule the day.