There were several turning points at Gettysburg.
IMO, Had Stewart’s end around not run smack into a wildly determined Custer at Cavalry field, he would have arrived in the Union Center rear at the same time as Pickett’s troops hit the Federal line on the ridge.
Also remember that there were conscription riots going on in several major Northern cities around this time, as well.
By what orders was Stuart suppose to attack the back side of the Union center on the 3rd day at Gettysburg.