I think CB's measurement is off a bit. From the bottom of the ramrod channel, to the bottom flat of the barrel, for him (& others), should be no more than about 3/16" to 1/4". It should only be thick enough for the barrel escutchions & pins and no more. When making guns largely by machine or perhaps making them fast, this 'fineness', 'frailty' seems difficult to do. It is easier to make them a bit heavier, chunky, stronger in the wood- more like a production gun.
All guns weren't perhaps uniformly skinny or frail - how much 'licence' does one give for interpretation? It's pretty much all speculation and personal wants or preferences. Some are set in stone while others more lenient.