This is no doubt what Graham believed, but it is quite incorrect.
The Federal artillery was not "silenced" by enemy action. For the most part they were intentionally shut down to give that impression, sucking the enemy into a disastrous charge.
A lot of the southern artillery fire was high, going over the ridge and into the rear areas of the Army of the Potomac. Caused some havoc there, but wasn't very effective against the actual Union positions.
Gen'l Lee's plan was excellent, but some one made a botch of it indeed. Had we carried those Heights, that Army would have been ruined. There were only two avenues of escape, and Ewell had one, and Longstreet the other. So that they must have surrendered or been cut to pieces, and entirely ruined.
Very large "had." Lee disagreed with Graham.
Couple months later he formally offered his resignation to Davis, accepting full responsibility for the defeat at Gettysburg.
A biographer said that he rose above victory by giving credit for Chancellorsville to Jackson, and he rose above defeat by accepting blame for Gettysburg.
No matter what, they won’t let anthing bad stick to Lee.