I think there are several objections that one can raise to Shaules' approach to posture. To me, the factor that he is missing is that freestyle requires core stability while rotating from one side to the other. It is not enough to simply keep your legs up while lying on your stomach. It turns out that the pelvic muscles are precisely the muscles needed to stabilize and transmit hip rotation to the shoulders, which is what powers the freestyle stroke.
That said, I don't think it's a good idea to take anyone's word on these things, just because they are an expert. I would try both approaches and see what suits you best. Sometimes, as your swim technique evolves, your perception of these issues may change, and if you feel Shaules' recommendations help you more than those of Richard Quick, then I would go with them. Just keep in mind that at some later point you my want to revisit Quick's approach and see if it starts to make more sense to you.