Huge difference Non. Stephens was a southern whig. It's kinda like trying to compare Olympia Snow and Phil Gramm.
Actually, I think that's a bit fallacious, since the overriding emergency of the war clearly beset Davis far more strenuously than it did Lincoln, so that your saying that his policies should be evaluated without reference to the war is a fallacy of accident: the exception should apply, rather than the generality. The world never saw a peacetime programme issue from the Confederate government.
Kang's argument is a little better, that Lincoln had wartime problems, too, and that is certainly true. But much of the North was untroubled by the war in a way that is just not true of most of the South (Texas being the exception there). And so it is possible to descry features in Lincoln's policies that would have been carried forward if there'd been no war; and to say with Kang that that isn't true, that we must apply the exception to Lincoln as well, is a converse accident and likewise fallacious.