When making comparisons about case capacity at least use the same powder to compare the 2 rounds. There are very real differences in volume of different powders which leads me to think that you probably don't handload.
To prove this point I am posting data from the Nosler reloading guide #4.
Using reloader 22 for 165gr loads for the 30-06
max 63gr -3002fps
using reloader 22 for 160gr loads for the 7mmremmag
max 63gr-3058fps.
In other words the 7mmremmag produced more velocity with the same amount of the same powder.Since the ballistic co-efficient is much higher for the 7mm bullet,the velocity advantage will increase with distance making iteven more efficient.Just proving that if you choose the right loads,you can make the data appear to show what you want it to as you did with the 30-06 load that you keep quoting.