Lots of western historians study history extensively and still don’t escape the ideology of their class. Even a well-meaning Marxist is prone to have bad takes on history depending on who they read because, let’s face it, not everyone has the time or the will to read and vet primary historical sources.
The essential thing is not necessarily to be a History Knower but to recognize that every social relation is historically contingent. That includes wage labor, the state, race relations, religion, etc. If it is social then it typically has a material basis which can change over time. Because they usually lack this perspective, non-Marxists are more inclined to have reactionary takes on both current and historical events, regardless of how much history they know.
One excellent book I’m trying to finish is Michael Parenti’s The Assassination of Julius Caesar. Just one example of how historians have distorted the past due to their class lens.
I do wonder how a historian who seems to understand history can then woefully misunderstand the USSR or other socialist powers. They know how to properly source something, how to interpret first and second hand accounts properly, how to spot an unreliable source, yet when it comes to the dreaded communism they just throw out everything they actually know about their field out the window.
You’d think that, and with the way he lectures you’d still think that he would know better, but nope, my man loves to gush about the Gulag Archipelago so that gives you an idea of where his views lie…