Accuracy: Little to none.

To begin with, it isn't even entirely by those two pastors, as it seems to have heavily plagiarized another work from two decades prior.

The publishing house, Canon Press of Moscow, Idaho, seems to specialize in publishing Evangelical tracts on topics such religiously inspired fiction by the likes of Kirk Cameron to convince people of creationism or a DVD on the death of freedom of speech whose cover is an LGBT activist painted in ominous red and black, carrying a chain-saw (with interviews with Ted Cruz, Dr. Ben Carson, and others). In other words they seem to be publishing non-specialist propaganda for the fringe of the Evangelical community. Not a serious publishing house.

Second, the two essential pillars of the piece are refuted, in one case, and irrelevant to most people, in the other.

The first pillar is that Southerners should take pride in the Civil War because slavery wasn't the cause at the heart of the conflict and because criticisms of slavery are largely exaggerated. Here is a great post by a mod refuting that argument in great detail.

The other pillar of their case is that:

The truth is, Southern slavery is open to criticism because it did not follow the biblical pattern at every point. Some of the state laws regulating slavery could not be defended biblically (the laws forbidding the teaching of reading and writing, for example). One cannot defend the abuse some slaves had to endure. None can excuse the immorality some masters and overseers indulged in with some slave women. The separation of families that sometimes occurred was deplorable. These were sad realities in the Southern system.

In other words, the primary mistake made was not following biblical slavery, which implicitly seems to be fine by the authors. If you believe the bible literally, maybe their detailed justification of a certain kind of slavery would be interesting or even pertinent. If you don't believe it literally (or just aren't Christian at all) their arguments on this point are completely irrelevant.

Both successfully sidestep testimony from slaves, as well as non-slave sources such as countless newspaper adds referring to scars from lashes, which contradict the version of history they want to spin: That abuses were isolated cases of bad apples. They cite whatever backs that up and ignore whatever contradicts it.

In short, there are surely more serious historical revisionists to read for 'the other side of the debate' than these two.

I haven't read Wilson and Wilkins' book, but I've read several reviews of it which, as far as I can tell, tear it apart. Here's one response from Rev. Jack Davidson of Eugene, OR, engaging with a number of Wilson and Wilkins' primary sources - from the Slave Narrative Project - and pointing out how they must be taken with a great awareness of context that Wilson does not exhibit.

Further, here's another response by attorney Thomas Alderman, explaining how Wilson and Wilkins grossly misrepresent the origin of the Civil War, which was indeed about slavery - a point also explained in great detail on this subreddit.

On a similar note to this, I just had a history discussion yesterday on this very same subject where we looked at the arguments made by James Henry Hammond (Letters to a English abolitionist). It's a good read for anyone wanting to know how southerners justified slavery at the time. I haven't read the source you shared op, but a brief skim through as shown me a few similarities.