Let’s say Ewell hadn’t siphoned off some of the artillery and the supply trains were close enough that Longstreet’s barrage kept up as planned. I’ve stood on Cemetery Ridge and that damned cornfield is still a literal mile wide. Could Picket have broken through?
What if Custer had not delayed Stuart? A pincer movement using infantry at the front and cavalry at the rear looks like it would turn the Union lines to chaos. Did Custer win the Battle of Gettysburg?