Maybe I overdo hyperbole.(1) The man who kept the ANV going through all those impossible times is in no way an idjit.
Quite frankly I have never seen the point to the Gettysburg campaign,(2) as a victory would have been worse than a loss.(3) (Stuck miles from anywhere, no food,(4) no munitions,(5) in danger of being cut off and sort of obliged to keep going)(6)
I just think Vicksburg was vital to the health of the confederacy.(7) Losing it means that the farce (Because of Matamoros and the ease of slipping stuff across the border) that was the Northern blockade all the sudden became very real. Bottling up Grant in Vicksburg (8) with a larger force is a really useful gamble.(9) Since no General in the Army of The Potomac is really going to chase after Lee, risking a corps to rescue Pemberton is worthwhile.(10)
Last point over again.... Lee did wonders with nothing, but he did have the problem of seeing the war as only Virginia. Not an idjit, but severely blinded in some respects.(11)
Cool response!
1) Maybe?
2) FOOD, plain and simple. If not for the massive amount of rations and materiel obtained from Pennsylvania Lee's army would have come out of the Winter of 63-64 every bit as ruined they were going through the winter of 64-65. A time when even true believers were walking off the line into the hands of the Yankees and taking the Oath of Loyalty to the Union. Devastating as the Gettysburg campaign turned out for Lee, it did reduce the AotP to relative ineffectiveness until the Spring of 1864.
3) A victory where? It would have required sloth on a level George Meade simply wasn't capable of. And things were actually likely to have gone much worse than they actually did OTL.
4) Food was the one thing (for once) he DID have.
5) His artillery munition supply determined much of what he did.
6) Indeed, where it not for Meade's caution (and the even worse caution of his corps commanders) Lee might well NOT have slipped away. Ironically, the absence in AotP HQ of the crippled Sickles may have helped Lee greatly. Despite whatever other criticisms that were richly deserved by Sickles, he seems to have been a rare officer to not have been afraid of Lee.
7) You ain't just whistling Dixie.

The superior level of conditions for Confederate troops in "Kirby Smithdom" (fresher uniforms, more rations, more guns, more ammunition) reflect what a harder time the Union could well have had with the Mississippi still under Southron control.
8) Not sure what you mean here by "bottling up?" Hold Vicksburg, you close the river. And you can't stop the Union from making landings at will north and south of such a strongpoint. Or by "bottling" do you mean "in the Vicksburg region?" That is, without taking the city?
9) At no time in the ACW did the South ever have to pay for being outnumbered as a country as they did at Vicksburg. Winning again and again in Virginia, stopping Union advances in the center (and even invading Kentucky), and holding up Grant on the Mississippi, SOMETHING had to give. The Confederacy had decided that the river herself offered enough natural barriers to hold off the Union Army with a
relative minimum of troops. They were wrong.
10) Lee used a two corps system. Sending one corps meant sending half his army. Even the likes of Ambrose Burnside could have pulled off a major strategic victory with half of Lee''s army 1000 miles away fighting near Vicksburg. Remember that the problem with Burnside was he was TOO aggressive.
11) In many respects, Lee took his duties as commanding general of the Army of
Northern Virginia all too literally. Jefferson Davis all but abjectly BEGGED Lee to go west, and every single time, Lee demurred. He would send the Georgian/South Carolinian Longstreet, but not his fellow Virginian, Jackson. Also, the Vicksburg Campaign really only got into high gear in the Spring of 1863. The AoNV (and all parts of it) were very busy at the time.