Actually Ron, while you are certainly correct in regards to modern (post WWII) shells, in the early days, especially with the smokeless powders of various types, behaviors, strengths, etc, they really did not KNOW how much strength there was in a hull so the brass head was there for strength. If you look at many early shell heads you will see they were crimped to the wrapped paper (cardboard) cases. This was done to prevent head seperation, which occurred from time to time.
As for the cases volume, black powder was bulkier, requiring more space for a given power of shell than with the smokeless powders. It would have been a short lived (or at best, unhealthy) individual that loaded smokeless powder by bulk vice weight. But there was a period of transition where I’m sure the foolish perhaps did perish.
Here’s a WRA LEADER shell from my collection, loaded with Ballistite, that shows a rather ‘beefy’ construction.