Well, this is an interesting and difficult question for me to answer, particularly as I'm self-taught. I'm not sure it's actually possible to ever quantify "accuracy" as a degree or percentage, as I always feel driven to by a question framed this way.

One thing about the Myth of the Jacobite Clans is that it is revisionist. Now, that's a word that often gets a bad rap, but in this case, it's really more benignly meant in that the book takes a look at a lot of assumptions about the Jacobites, their motivations, and their, well, provenance and brings evidence to bear that the traditional viewpoints are lacking. Some of the more interesting points are that "clan" structure was not as strong in 1745 as England largely took it to be--that strict structure on family hierarchy had weakened by that point and it's therefore inaccurate to talk about "Jacobite Clans." This is the title assertion of the book, even, and I think it can be readily demonstrated by looking at source documents. There are several instances where a clan chief refused to come out for the Prince, but a younger leader or cadet branch of the clan would. For example, Alexander MacDonald of Clanranald flat-out refused to answer the call, but his relative Aeneas MacDonald was one of the Men of Moidart and Ranald MacDonald the Younger of Clanranald also came out. You can see similar things with Cameron of Lochiel, or even the split in Lord George Murray's own family--he and two of his brothers were staunch Jacobites, but another brother and their father were completely against it. As to the later idea of the "clannishness" of the Highlanders, More Fruitful Than the Soil makes a case that the Duke of Argyll manipulated London's perception here to allow a high degree of nepotism in the Highland regiments, thus allowing many disgraced former Jacobites to ameliorate their images.

Another point the book makes is the frequent designation of the '45 being a "Highland" struggle is misleading to inaccurate, as the definition of "Highlands" has shifted considerably over the years. There's also a considerable degree of nuance in who fought for what reasons. I don't recall if the book went into detail on that, but I have in other comments.

It's been quite some time since I read that book and this is what stands out in my mind right now. If you have other more specific questions, I can do my best to answer.