The insistence on appeal to authority/appeal to credentials is not only based on the false premise that no revisionists have any relevant training, it is especially inappropriate in the field of history. For certain fields (e.g., medicine), there can be a noticeable gulf between professionals and laymen. Getting fully trained in medicine or science is generally too expensive and too much trouble for a layman. But history is of general interest and is relatively accessible to outsiders/non-professionals. In fact, many well-regarded historical works are written by non-academics. Here is a short summary bio for Max Hastings (from Wikipedia).
Sir Max Hugh Macdonald Hastings is a British journalist and military historian,[2] who has worked as a foreign correspondent for the BBC, editor-in-chief of The Daily Telegraph, and editor of the Evening Standard. He is also the author of thirty books, most significantly histories, which have won several major awards. Hastings currently writes a bimonthly column for Bloomberg Opinion and contributes to The Times and The Sunday Times.
He's referred to as a "military historian," yet his background was in journalism. He apparently did not even finish university. It seems a fair number of historical writers have been journalists (foreign correspondents, in particular). And as a rule these types are probably better writers than the average PhD historian.
In thinking about what distinguishes a credentialed historian from a non-credentialed one, here are the things that come to mind.
Time Obviously, if someone is paid to research something and does this full-time, that is a huge difference vs someone doing research in their spare time on top of a normal job.
Access to Sources An academic will have more ready access to sources (digital subscriptions, faculty library privileges, research assistants, etc). Research trips are more feasible (the layman with a regular job would have to use vacation time to visit archives). They have a network of colleagues.
Historical Training The curriculum in a history PhD will teach historical methods. This is fairly minor, imo, since you can easily learn this via self-study.
There are others that could be mentioned, but most of them boil down to time and resources. For instance, a professional historian specializing in a particular area will have studied the relevant languages (although I will say the foreign language exams for history PhDs are quite basic). For the layman, this can be a major barrier, especially for less commonly studied languages. Most laymen will not have the time to make that sort of investment, but it's of course not impossible. Many revisionists have been native German speakers and obviously have way better German than Anglosphere academics. David Irving has very good German which he learned by living in Germany, not through school.
Correlations
The reason appeal to authority is a fallacy is because credentials are neither necessary nor sufficient to argue for a given proposition. It's a fallacy because if the authorities are right, then it should be possible to explain in detail why they are right and that reasoning and evidence should hold up regardless of who is making the argument. However, we don't want to take this idea too far. In fact, some people are more informed than others and on any particular thing most people aren't informed at all. Even on the far-right which often countersignals the establishment, we see the most celebrated thinkers are (surprise!) people with PhDs. Kevin MacDonald, Andrew Joyce, Greg Johnson, Thomas Dalton. That's not an accident.
Human Capital Theory vs Signaling Theory of Education
While there can be a correlation between academic and professional background and quality of research and opinion, it is important to realize there are many exceptions and it probably isn't entirely causal. We see these sorts of relationships in the labor market. Statistically, education correlates with higher earnings. However, part of this is purely a selection effect: people who complete more schooling are smarter to begin with, on average. The average IQ for a high school drop-out might be 90 or something. For college graduates, it's a bit above average, say 110, varying considerably by school and major. Graduate programs are more selective still, although things start to break down a bit here. Engineers typically get "only" a bachelor's degree yet they are on average probably smarter than a middle school teacher who gets a master's in education just to get a salary bump. According to the
signaling theory of education, much of the correlation is due to selection effects (especially for brains). If this is the case, then we should certainly not be close-minded about education and professional background.
