It seems to me that having to polish all feedback to a publishable level of quality would (greatly?) reduce the amount of feedback someone could give. I've appreciated informal feedback that I've received in the past and if that was the bar that needed to met I would have likely never received anything back.
I'd agree that, in general, you shouldn't necessarily aim for the same level of polish in feedback that you would in a piece for publication. Here, though, I think the excessive length of his comment undermines the credibility of his feedback and contributes to the sense that he's piling on the criticism.