Keith,
McPherson and Davis probably do not qualify as "Southern leaning" historians. But, really, who does and why?
It would seem that some are looking for historians who advocate the same political or ideological viewpoints of history. The phrase "Southern leaning" suggests someone taking a preference towards the South. Well, preference in what way? I think the answer is obviously supposed to be, prefer the South's political, economic, social, and ideological positions during the war.
But, as I and some others here have explained, this is not what historians generally do in the field. Universities do not recruit or try to train new cheerleaders for "pro-Union" or "pro-Southern" advocacy. We can find examples of historians delving into something like this in outside contexts (such as the modern dispay of the CBF, etc.), but that is generally a separate issue.