Reading Sear's Lincoln's Lieutenants ....
It becomes supremely obvious that the reason the Army of the Potomac was unsuccessful for so long results from its proximity to Washington. The further away from the "seat of war" the greater the positive results. This is not a coincidence. The Army of the Potomac's commanders in chief were subject to so many differing and varied instructions, from the great and obvious, to the mundane and minuscule.
For example, Meade sees an opportunity after Gettysburg to turn Lee's right flank, he draws up a plan, has to send it to Washington, and it is not approved.
In the West, Meade draws up his plan, issues his orders, and pounces.
That, therein, lies the difference.
Washington; Lincoln, the cabinet, and the Committee on the Conduct of the War are mostly to blame for the Army of the Potomac's struggles.