It's interesting that you say he's learned to "rehearse" whatever he says. What makes you think that? Of course he can rehearse the presentations he makes on Youtube and on live streamed shows, but I doubt anyone can kill the inherent spontaneity that comes with speech, at least in most contexts. I downloaded his "D.A.M Strategy" to have a look yesterday, and it does seem a bit thin. Most of the strategy revolves around positive affirmations (such as telling yourself "I am an amazing" speaker). I guess this is what you mean by Williams "[killing] his 'real' self", but that seems to be a negative way of framing it. If you can drill your subconscious to remove conditioned beliefs that you're a poor speaker, and reinvent your identity as a "stutterer" in the process, I don't think you're killing your true, authentic self. Identity is a fluid concept. Saying that though, it's the first time I've heard of positive affirmations working so effectively. I'm quite sceptical.