Lee operated under great disadvantages in number of men and material.
He did amazingly well for the circumstances.
He came very close to winning.
All generals have the strength and weaknesses of the tactical situation they are confronted with. And as I said Lee was a very good General but he certainly made major mistakes. And he didn’t have the ability to learn from his mistakes all that we11. The “audacity” which gave him his greatest victories also contributed to his worst defeats. Once Grant started his Overland campaign, about 6 weeks later Richmond was invested, the army of Northern Virginia was in a siege and for all practical purposes the war was lost for the south. Certainly having to deal with the consequences of the defeats of lesser southern generals (Bragg, Hood) didn’t help Lee. Had Braxton Bragg exploited his victory at Chickamagua and destroyed Rosecranz’ army; the situation Lee faced in 1864 would have been much different.
He lost Gettysburg because he fought it as if he still had Jackson, who died only two months before.