I think Scott Adams wildly overestimate the power of conversational hypnosis.
First of all, yes, there have been prominent public figures who are well versed in the art. But that's no argument at all: how many people are trained in conversational hypnosis (or NLP, or what have you), and how many of those are hyper-successful? And how many hyper-successful people are not trained in Ericksonian hypnosis? You could even make the point that Steve Jobs and Bill Clinton were successful despite being trained in that art.

There's also something to be said about linear return on persuasion. If you are 2X more persuasive than your opponent, would you gain twice the supporter? I'm not very confident in this hypothesis too.