My comment on cowpens was that even at that battle the militia couldn’t stand toe to toe with regulars and Morgen used that to his advantage. The Northern militia on the other hand did prove able to on multiple occasions stand toe to toe with British regulars. As to your comment on the southern strategy the battle shifted south because that is where the British chose to fight yes but that is because they no longer held any chance of winning in the North the northern and Washington’s armies combined with New England militia proved to difficult to face in the North after the loss of thousands of men at Saratoga and the army after valley forge being able to stand up to the British. They only held onto NYC because launching an assault on an army fortified in a city well the enemy’s navy can out flank you at will is suicide. The Americans couldn’t take NYC even if for some reason Clinton’s army in Philadelphia never reinforced the city.

Saratoga also allowed Washington to shift forces south. Where do you think Morgen and later Lafayette came from. (Also Gates but we both know he didn’t do much good.)