I don't see how getting more people interested in ancient history and geology is a bad thing. Part of the reason Graham has the wiggle room to make the claims that he makes is that the subject is relatively unstudied.

Obviously there is actual science taking place in the field and has been forever but funding for that kind of thing is notoriously difficult to come by compared to many other fields. Getting grants to study the distant past for essentially no reason other than curiosity is not a priority within an economic system that prioritizes profit over all else. The best way to break through that particular obstacle is getting more people to pay attention and ask questions. If we need a benign conspiracy theory about "big geology" hiding the truth from us to make that happen then where's the harm in that? The vast majority of people prone to conspiratorial thinking are already farther down that rabbit hole than Hancock's ideas will take them.

Additionally, actual scientists would do well to learn something from Graham about presentation. Despite what you may think of him, the way he talks about the subject resonates with people. People don't want hear a regurgitation of facts in a research paper. Speculate a bit and get people excited about your future work. You don't need to go to the extremes that he does but don't refuse to branch out from what can be conclusively proven today either. Talk about your theories and what you're hoping to find / learn just as much as you talk about the results of your research.