The point of proof is to see if a given action/barrel combination is sufficiently strong to do the job it is intended to do.
This is why our guns don't all weigh seven pounds and digest 3" magnum loads.
Barrels have got thinner as technology allowed them to. Barrel profiles changed as gunmakers gained a better understanding of where thickness was needed and where it was not - and how a barrel aided handling by being balanced a certain way.
If someone comes up with a 'super steel' that can comfortably handle proof loads when 5 thou thick, will there still be calls for 20 thou in new guns? Some guns were made in the past with barrel walls a minimum of 36 thou (I have some) and others originally measured only 18. All passed proof and are safe to use as intended.
Why carry a heavyweight when you only need alightweight?
