Hancock's primary claim is that the ancient Egyptian, Mesopotamian, and Mesoamerican civilizations didn't arise independently and that instead they were guided by the survivors of some advanced ice age civilization that got destroyed. This is pseudoarchaeology and pseudohistory whether or not he claims to be an archaeologist or historian; being a "journalist" engaging in conspiracism isn't a shield against the claim. Actual archaeologists and historians dismiss these claims as in order to make them you have to cherry pick evidence while dismissing evidence that disagrees with your conclusion. Do you think it's more likely there's a conspiracy that encompasses the entire fields of archaeology and history to "hide the truth" or that these obvious liars are lying?

That there's much we have yet to learn about our history doesn't mean we should entertain the trite tales of cranks. Many of these myths (ancient aliens, Atlantis, lost civilizations) end up becoming extremely racist and/or anti-Semitic once you get to the core of the conspiracism motivating them.