I think the truth is somewhere in between. I don't know the timeline for when Ken started teaching on his own, but I doubt it was when the unit began. He did go there a lot at one point, and I remember him saying that Leatham was training them too. According to Ken they were bringing in anybody they thought could teach them something useful, meaning not just firearms. I never heard him say that he developed OTC or that they relied on him in some special way.
One of the things that I think some people don't appreciate about Ken is that he's been around a long time so he can explain a lot of history. He has also done training classes for a large number of agencies and some foreign military units. He is very much against what he calls enter-trainment, so if you want to run and gun you won't like his classes. FWIW you also won't like Tom Givens.