It’s interesting that Longstreet failed on the second basically due to failed recon & a misconception of where the federal left flank lay. It’s true Meade had to send in significant reinforcements to bolster 3rd Corps but having the interior lines helped him accomplish this. I won’t second guess history here as it’s interesting enough… but it is fun to contemplate.
This excerpt is from a lengthy Essay by license Battlefield Guide Michael Phipps, regarding leadership at Gettysburg & Dennis Hart Mahan’s influence on American officers tactics. Covers a lot of ground, but it’s interesting thesis if one has time to read it.
“Another passage of Mahan’s tactical manual is almost a word-for-word copy of Lee’s plan of attack for July 2, 1863 at Gettysburg:
‘The main effort of the assailant is seldom directed against more than one point of the position; that one being usually selected which, if carried, will lead to the most decisive results; as, for example, one of the flanks. ... But the main attack is always combined with demonstrations upon some other point; both with a view of deceiving the assailed as to the real point of attack, and prevent him from withdrawing troops from other points to strengthen the one menaced.
Lee, on the second day of Battle at Gettysburg, gave almost these exact orders to generals Longstreet and Ewell. Longstreet was to make the main attack south to north, guiding on the Emmitsburg road, and strike the Union left along Cemetery Ridge. Simultaneously, Ewell was to demonstrate against the Union right flank on Cemetery and Culp’s hills. The reasons why this battle plan did not develop into the battle actually fought are complex and well documented, and I will not discuss them here. But it remains an irrefutable fact that once Longstreet launched his attack on July 2, Meade responded by sending almost his entire army to the southern end of the field. In the north, Ewell’s entire Rebel corps, supported by a large portion of A.P. Hill’s corps, was opposed only by Greene and Carroll’s small brigades and the decimated remnants of the 1st and 11th corps. Ewell and Hill had a two-to-one numbers advantage. A major assault by the Rebels on Cemetery and Culp’s hills, instead of a diversion, may have cut through Meade’s weakened right like a knife through butter. What could have happened on the Union right that day certainly played as large a role in the outcome of the battle as what did happen in front of the Round Tops.”
http://npshistory.com/series/symposia/gettysburg_seminars/9/essay1.pdf