To be fair, he always states: "I am not a historian".
So if you listen to him as a storyteller, you will have a great time, and you might learn something along the way.
However, never take the book he's actually using...most of the time it's plain outdated.
As you say, you can't really blame a guy who says 5 times per episode that he's "not a historian", but plenty of times I just can't help and wonder why didn't he spend 30 minutes extra researching a topic and choosing better material and sources. The only answer I got is that bad material makes for better stories.