If Lee stays exclusively on the defensive, he's basically a better version of Joseph Johnston. Johnston almost lost Richmond in 1862, wasn't aggressive enough to aid Vicksburg (not that Pemberton helped him at all), and all but lost Atlanta in 1864. If Lee doesn't take the offensive in June 1862, Richmond's fate is sealed. Once McClellan brings up his siege guns, it's over.
The problem with Lee is that he won a lot but just couldn't pull off the wins when he really needed them and when they really would have mattered. That doesn't make his strategic philosophy wrong, just unsuccessful.
Ryan