John Sian did not really prove anything wrong about the papers he quoted in that article. He simply highlighted some myths about DF as follow:
Here's one of the paper he referenced, if you read the whole thing, you probably wouldn't hold Dick Pierce responsible for the myths JS cited, as JS himself said "READ THE PAPERS MORE CLOSELY!"
It seems to me it's a case when people, including Mr. Siau, tried to make their cases by emphasizing certain points. Mr. Pierce mentioned the benefits of higher DF, without identifying the details, probably because he wanted to debunk the one myth, that DF was such as major factor, and Mr. Siau appeared to be critical of Mr. Pierce paper, because he might have been trying to debunk the other myth that DF wasn't much of a factor. To me, both could have done better by reminding their readers not to jump to their own conclusion, unless and until they read the papers/articles in their entirety and understood the contents fully.