Why do you think Winchester's claim that fluting increases rigidity is not valid? It's actually basic engineering. Take a piece of paper slide it slowly off a smooth desk surface until it droops—mark that point with a pencil. Now crease that same paper hard and flatten it back out to leave a "rib". Do the same... slide it off the desk and see how far out it gets. A square bottomed flute is way stiffer than a round bottomed flute and a properly fluted barrel is way stiffer than a round barrel regardless of profile/weight.