I’ve seen some criticism of Dan Carlin’s work on multiple occasions on this sub. He identifies himself as a “fan of history” yet he seems to have a vast amount of knowledge across multiple subjects, far more than the average person. So, why does he fall short of being a historian? What qualities does one have to possess to be identified as a historian?
Because knowledge alone does not make a historian. It's not just about 'knowing' a lot of stuff about your chosen topic'. Frankly, I'd even say that having a lot of knowledge up front isn't even much help, because there is a lot more to it than just 'knowing things'. This is a lot easier to see when one cracks open an academic history work, and what a historian does to present the case they're making.
Not having listened to Carlin, I won't make any comment as to the man's qualifications or virtues or shortfalls. If he has a bit about wells or similar water technologies, then sure, maybe I might (largely to pillage his source list - I need more books, dangit); for the meantime, I'll refer you to our latest Carlin thread, which outlines some general and specific cases of where he goes wrong and why. As to your larger question of what makes a historian, here's another two threads. u/crrpit has some thoughts on the matter, and I myself have also answered the same question previously.