How good was Lee's Army of Northern Virginia?

During the time that Lee, Jackson, Longstreet and Stuart were together, here were the results:

Second Manassas, August 28-30, 1862
North - 62,000 troops
South - 50,000
Clear Southern victory

Antietam, September 17, 1862
North - 75,500
South - 38,000
Tactical draw, strategic Northern victory
But North had copy of Southern battle plans

Fredericksburg, December 11-15, 1862
North - 114,000
South - 72,500
Clear Southern victory

Chancellorsville, April 30 - May 6, 1863
North - 133,000
South - 61,000
Clear Southern victory

Notice the difference in troop strengths, and keep in mind that the North was vastly better supplied than the South.