Things may have been different if Stonewall Jackson had been there. Lee relied on him quite a bit.
Perhaps. Jackson has been mythologized. People forget his failures. He disappeared during the battle of 7 days and he was the only southern General whose lines were completely breached at Fredericksburg. Not saying he wasn’t a good General, he was. But he had his failures.
Jackson was really good in the Valley and in the Wilderness of northern Virginia, and was just OK everywhere else. He performed poorly in the 7-days. It would largely have depended on “which Jackson” showed up in Gettysburg. I would say that Jackson would have likely taken Culp’s Hill on the first day, so the “real battle” probably would have taken place at the Pipe Creek line a few days later.