It’s hard to say if Lincoln’s presidency turned out well or not, as we have nothing to compare it to. Maybe another president could have furthered the abolition of slavery without civil war; maybe another would have handled things better.
But to say that the US Civil War set the course for all human history since then? That is too much–think about it. And the centralization of US political power was, I fear, the beginning of the end.
Sure we got something to compare it to.
We have the past to compare it to, and the present.
If Lincoln would have lost the Civil War, that means that the power of America would have been halved, or quartered, the West would have been settled at least as slave as free (probably more, as southern values, without slavery dominated the Wild West),and the idea of racial enslavement and a caste system of human rights would have been there in place of what America has become.
The other president that would have come to the fore if not Lincoln would have been the likes of Stevens or some other slaver. He would have done things better for the whites of the Southern but the idea of all men being created equal would have gone down the drain to the extent that he was successful.
Slavery and the acceptability of the right to own other humans was as common as mud the world over before the Civil War settled the question in blood. This is no small matter when it comes to the idea of universal human rights coming to the fore in the first place.
It is not hyperbole to say that the Civil War set the course of events since then, because a powerful America, the undivided America that settled the continent, and played the determinative factor in the era of World Wars that followed came out only because America emerged from the Civil war united.
Without Lincoln, or a president who did exact same thing as Lincoln, the whole course of human history, with democracy and human rights coming to the fore, would not have happened, because it is America that is central to those efforts.
There really is no way around that, no matter how many maybes are entered into the equation.