As for Lee:
I have a complicated opinion of a complicated man. His letters to his sons and other family members show he really agonized over what he would do if Virginia chose to secede. And I can respect his decision to resign his commission rather than accept command of an army that would invade Virginia and kill Virginians. His family went directly back to the heroes of the Revolution - his father was Light Horse Harry Lee - and the Custis and Lee families were "First Family of Virginia!" (Free 1776 reference). So it was just socially, familially and emotionally impossible for him to do it. George Thomas did - and paid for it by being declared 'dead' by his family and never speaking to them again.
I get all that. We are sometimes under intolerable pressure to do what society, family and friends expect of us.
But then he accepted a generalship in the Confederate Army. In other words, he faced a great moral test... and muffed it, because there is no evidence that he had any zeal for slavery or Confederate independence.
He required his men to comport themselves well - as well as any men of the war and better than most. He surrendered the Army rather than ask the men to scatter into guerilla bands, and he was gracious in defeat. When the war was over, he retired quietly to Virginia, turned down offers of public office and made known his view that the war was over, the judgement of the Almighty was rendered, and Southerners must accept it. That did take moral courage, in a post-war South.
So there is a lot to admire there, but just as I can admire parts of Rommel's character while despising others, I do believe Lee's putting on the gray coat was a weak, expedient moral failure - at best a naive one - from a man who, otherwise, worked very hard to do what his family and position required. Lee was supremely dutiful, in every moment of his life except one.
Lincoln post-war would have had to fight both the Radical Republicans and, as Southern states were re-admitted to the Union and sent members to Congress, a shrinking Republican base of support. He might well have found himself walled off by both sides and ineffective.
People who worked with him over long periods of time often came to respect and admire him. But he never had any success changing a Southerner's mind, or a slave-owner's mind. I can say I think Lincoln would have been a better post-war president than the Southern-apologist Johnston. But given our 150-year wallow in Lost Cause treacle, I think the nation might have been better off if the Radical Republicans had been given their head to Reconstruct the South along the lines of equality. The medicine would have been awful... but so is the disease.