As a British person who doesn't know about American history between the establishment of the Colony of Virginia in 1607 by the Puritan Stuarts up until 1900 excuse me if this post has any inaccuracies.
I know of Ken Burns's 1990 series The Civil War which (just looking at the amount of threads on this subreddit alone referring to the series) was extremely well received by the public, non-academic crowd with it causing a resurgence of interest in the topic as well as receiving countless awards. The series (from what I've read) made author-historian, Shelby Foote a household name in the American public & academic circles. What was the state of ACW historiography prior to Burns's documentary? Disregarding Foote's work.
Foote's 3-part tome on the ACW, The Civil War: A Narrative was published (1958 - 1974) several decades before Burns aired. By the time Foote rose to fame in Burns's series had the main topics of conversation surrounding the ACW's historiography changed in any major way? Possibly causing Burns's use of Foote as the main consultant to flaw his series & make it outdated before it had even left nappies? Did historian's opinions of Foote's work change (for better or worse) after 1990?
Prior to 1990, What caused the lack of public interest in the ACW? Was there also a lack of ACW coverage in history lessons? What was it about the series that made the public sit up and listen?
Did Burns's series change American perceptions of earlier & later causal/consequential events (e.g. American Revolution, War of 1812, Reconstruction era, Rise/Resurgence of the KKK: 1865-1870's, 1915-1944 and the Civil Rights Movement)?
And lastly, can Foote's work & Burns's series still be used as introductory tools for a newcomer wanting to learn about the ACW, it's causes & effects?
There is a lot going on in this question, but briefly, the state of historiography concerning the American Civil War in 1990 could best be described as being dominated by a neo-abolitionist interpretation that began gaining steam in the 1960s, and is perhaps best represented (in a 1990s context) by James McPherson's Battle Cry of Freedom published in 1988, around the same time that Ken Burn was preparing his documentary.
While I'm being reductionist here, neo-abolistionists were insistent upon returning to the narrative the singular importance of slavery, not simply for Southern desires to maintain it, but for the North's moral desire to see it vanquished as well. Much of this criticism was geared towards the revisionist scholars of the 30s and 40s who saw the Civil War as the product of a selfish, impulsive group of political elites who's inability to compromise resulted in hundreds of thousands of deaths and implicitly carried strong anti-war undertones. Kenneth Stammp's The Causes of the Civil War, which received a final revision in 1992, is a good source for understanding these transitions. It best represents the exact nature of the literature in 1990, and it is worth reading if you want to quickly familiarize yourself with these debates leading up to 1990. You can find it here:
The second aspect of your question, I am little more unsure of. But I can say that Burn's documentary is basically in alignment with a neo-aboltionist interpretation, but those types of historical arguments are downplayed a bit in order to focus on the details of battles, personal struggle, courage, adversity, etc. Things that the average public would find more enjoyable to watch, and that approach certainly has it advantages/disadvantages.
By bringing up Shelby Foote, you are correct to speculate that perhaps Burn's documentary was already out of date before it was conceived of. To this I would say yes and no, predicated on my previous paragraph. Foote's work was for a general audience, is well researched, masterfully written and quite engaging. It really is not "argumentative," and is rather neutral in tone, in much the same way Burn's documentary is.
I'm not sure about the progression of historian's thoughts about Foote's work, but as someone who is engaged in the ACW scholarly community, most will praise his work for its engaging narrative, but are quick to point out its limitations as a scholarly source, and that the work is best suited for public consumption rather than academics.
On the other side though, many are resentful of the renewed public interest in the Civil War, because it gave rise to "civil war buffs," who are more interested in battlefield statistics than understanding the cultural implications of the war's outcome in relation to race, racism, slavery, etc. I remember at panel discussion about military history at the Southern Historical Society's annual meeting a few years, exploded into a heated debate about Civil War buffs in the classroom, and what to do about them.
While I did not address everything you asked, I hope this response helped a bit. And hopefully others can modify/or fill any gaps in my response.