Some of his claims are quite far-fetched and esoteric. However, even Michael Shermer, head of Skeptic magazine, recently admitted (https://twitter.com/michaelshermer/status/123755946996742144...) that there is some plausibility for the younger dryas impact hypothesis, which is currently an important part of Hancock's lost civilization claims. Such a major catastrophe would of course have a reset effect on any existing advanced civilization. This alone is not proof that there was one, of course.
Dismissing a hypothesis just on the basis of sticking to the baseline works in 99% cases. Then there are the 1% Galileos and Keplers which get dismissed too because their argument is not heard out.
And yes in such limiting circumstances you need to develop a fringe fan base or let your findings die out.
As John Anthony West puts it
"... it was Victor Hugo who wrote the famous line there's one thing stronger than all the armies in the world and that is an idea whose time has come. You know that line was that the second strongest thing in the world is an idea whose time has not yet gone ..." [1].
