First, Lee was responsible for the Army of Northern Virginia, and can hardly be blamed for southern defeats elsewhere.
Second, Lee fought his part of the war the way Lee wanted to fight it -- sometimes over objections from Davis & others in the Confederate government. Indeed, at their conference in May 1863, where Lee proposed to go north to Pennsylvania, others wanted him to dig in behind fortifications while sending part his army out west to help at Vicksburg.
Some posters here have even suggested Lee was wrong and the others right, and that Lee's "aggressive defense" was the wrong strategy for the South.
Be that as it may, I don't agree, but my point is: Lee's "aggressive defense" strategy was HIS strategy, not someone else's, and Lee continued it until near the very end, when his forces were too weak to do anything but dig in around Petersbug.
Here's the bottom line: no matter how brilliant Lee & other southern generals were, or how gallant their troops, the South was doomed to lose in the long run. Unless... unless they could somehow early-on convince the North it would never defeat them, and so must negotiate a compromise settlement.
The possibility of doing so ended with the loss of Vicksburg, and in Lee's defeat at Gettysburg, in the summer of 1863. So, Gettysburg was, to quote my trusty source, the South's "Last Chance for Victory."
Richard Bensel has a great book called "Yankee Leviathan" where he looks at the relative levels of freedom especially in industry and entrepreneurship between the two sections. Virtually all of the new weapons came from the private sector---the Sharps, Spencer, Gatling Gun, one of the heavy guns (Dahlgren or Parrott), Ericcson's Monitor, Hunley's sub, even the signals the North used with the flag system were a private sector invention by a NY doctor. The point is, with a much bigger society to begin with (22 m vs. 9 m, of which only 6 m were free whites), the smaller society would have had to have been far more innovative and freer economically---but it wasn't. Quite the contrary, Bensel showed, the S. had higher taxes, more confiscation, less "free speech," and so on. So hoping to "leapfrog" the North technologically was impossible.