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I don't know much else about him, but nothing in this story reads to me like someone going off the deep end. It sounds like someone who picked a perhaps-unfortunate hill to die on, though if you aren't willing to take risks to argue against silly rules when you're at the top of your game then when will you, but not someone losing his faculties.
He hasn't gone off the deep end (past tense). But is it a process currently in progress? Only possible to say in hindsight but does certainly seem possible.
We are animals and eventually the brain will rebel against extreme repetitive mental effort that is perceived to be at least partially useless (and given he's already been the world champion, it's easy for part of him to think there's no point in training).