They consider it non-repudiable not because of DKIM, it's just a common misconception. People believed that before DKIM. They will still believe it if Google discloses its DKIM keys.
They totally should not believe it, though.
> So if I can't give the exact number of times that DKIM has helped in dispute resolution, then my argument "has zero basis in reality"?
Of course that's not what I meant, I don't care about exact numbers. Just give me some evidence that DKIM is relevant to solve disputes anywhere else other than in the minds of HN commenters. Otherwise your claim that the world is better off now with non-repudiable email has no basis in reality.
> they are choosing non-repudiation over privacy
They totally are not. They have no idea what are the properties of email. As an example, a non-tech friend of mine was once surprised that email does not provide any confidentiality.