I think the mistake he's making is in that while his hierarchy is correct in that one bug from a category further up is far worse than any bug in a category bel

I think the mistake he's making is in that while his hierarchy is correct in that one bug from a category further up is far worse than any bug in a category below it, if you have many more bugs from lower categories they can start to become problems on the scale of a few bugs higher up the chain. Constantly dealing with typos is a great example because one or two would not be a big deal, but they can add up to significant mental effort and time loss.