Defy has more Zinc/Boron and PHM has more Moly and higher TBN. AGree the PHM is for "newer" high mileage vehicles while Defy is more for older vehicles.
Two of the best HM oils available IMO. The Pennzoil is indeed thicker and otherwise clones PYB's wonderful add pack. The Maxlife has a very stout cleaning package though (about 2600 ppm calcium/sodium vs PHM's 2400 calcium).