Lincoln is underrated because he was willing to go to war with an extremely rich and powerful south.
Yall need to understand, they didn't just say "but the blacks!" To motivate white people to take up arms in the south. The civil war wasn't just about keeping slavery legal, it was about the EXPANSION of slavery. This means the south was willing to unilaterally expand into Mexican land and declare war on Mexico to grab more territory.
White people who had been in America and were hoping to advance from working class to upper class knew that if slavery expanded, they could grow their businesses and maybe even earn enough to buy land and some slaves for themselves. Hating black people was a motivator, but an even bigger motivator was the possibility of going from being a descendant of English peasants going back 2 generations to becoming a member of a new aristocracy.
Lincoln didn't particularly care about black people, but he did not want America involved in another war, he needed to stop the south from acting on its own and getting hundreds of thousands of people killed.
So you got the civil war. Lincoln had two goals:
1. Prevent a war half the country didn't want.
2. Find a way to either deport the freed people to Africa or to create a framework folding black people into American society.
He was killed, but had he survived America would have been a VERY different country. The southern strategy literally would not exist and the south itself would have become a much better place to live.