I bet coach's rack weighs twice that of a powertec or powerline amazon special.
The outside diameter of the tubing means nothing once it exceeds 2 inches (50mm approx).
The important thing is the wall thickness of the tubing which should be 1/8" (just over 3mm) or thicker.
All imported racks from China use Chinese metric steel so they are often only 2-2.5mm in wall thickness.