That is the opposite of my experience... I have found that the larger the bore and the (generally) slower the cartridge the LESS the velocity loss per inch of barrel as it is shortened...
I think you're on the same path: The bigger the bore, generally speaking, the less velocity loss for reduction in barrel length (how many long barreled .458 Winchesters are built to get some useful increase in muzzle velocity?). Again, this is generally speaking because there are very quick burning powders which burn much more quickly with x amount of barrel length, and there are very slow burning powders that require x amount of barrel length to burn - so it isn't a binary binary comparison.
Homer Powley, who worked as a ballistician for Frankfurt Arsenals, was writing about expansion ratio (and other internal ballistics issues like chamber pressures) for handloaders back in the mid/late 1960's. I bought several Powley slide rule type ballistic computers in the early 1970's to help me with load development.
For example: compare the ubiquitous traditional moose load in the 30/06, a 180 grain bullet of whatever manufacturer, to the same 180 grain spitzer design bullet in the .358 Winchester. In the same 24" barrel length - but with the .358 Winchester's smaller powder capacity. For comparison purposes, it's hard to find reloading manuals that use the same barrel lengths and also use the same powders in both - because they optimize the best powder choices for maximum muzzle velocity with the case capacity and expansion ratio. Velocity sells...
30-06: 2700 to 2800 fps, using ~ 53 to 59 grains of powder
358 Win: 2760 to 2830 fps, using ~ 45 to 50 grains of powder
So, slightly more velocity for the same bullet weight out of the same length of barrel - despite smaller case capacity. Expansion ratio. (If the subject wasn't the 358, the more similar comparison for the purposes of expansion ratio would by the 35 Whelen versus the 30/06. The same weights of powder charges in the same length barrel will now have several rounds delivering close to 300 fps more muzzle velocity for that same weight bullet)
So identical weight bigger bore bullets out of the .358 will exit the same barrel length going faster using less powder - but also with lower ballistic coefficients with the same spitzer form factor, which will immediately turn off the long range crowd. And slightly less recoil, of course, when you are burning less powder to get the same weight of bullet out of two rifles of the same weight. That's a plus for many, especially those who decide they like light hunting rifles.
You can play with ultimate powder selection for the resulting highest MVs in each rifle (assuming that is also the powder that groups best), and then furiously figure out the differences in the bullet drop in each chambering with that same weight of bullet at 300 yards (or whatever), and then do more calculations to figure to the last foot lb. what each delivers when it meets moose...
However, 180 grain bullets at anything near 2700 - 2800 fps out of a 30/06 have been putting moose in the family freezer at moose shooting distances for about a century. As will that same 180 grain bullet out of a .358 Winchester going slightly faster at the muzzle anywhere out to 300 yards if the rifle of the owner can shoot that far.
But as far as the issue of expansion ratio goes, you can get the same weight and same design of big game bullet out the end of the same length of .358 Winchester (until the point where the bullets start eliminating useable case capacity) as you can out of a 30/06 moose rifle. And that same expansion ratio is also your friend in bores/case capacity where the faster powders are an advantage if you prefer shorter hunting barrels.
Which leads back to the previous question of whether a longer barrel on a .358 Winchester is worth it?
I'd say it's worth it, depending on how much bullet weight you believe is necessary to kill a deer, an elk, a moose, etc.
If you believe that a 180 grain bullet will do the job out of a .358 Winchester just as well as it will out of a 30/06 (and the extra couple of inches of barrel length doesn't offend you), then it's worth it.
On the other hand, if you believe that unlike the ubiquitous 30/06 that kills just fine with 180 grain bullets, the 358 Winchester needs bullets of 250 grain or heavier to reliably kill moose and lesser creatures, then after you've surrendered all that case capacity to load those longer heavier bullets, my guess is that the resulting muzzle velocities are going to leave you with little velocity gain at the muzzle.
Other than cast hunting bullets of 225 grain and up out of the 358 Winchester, I've never understood the the factory 225 and 250 grain loads in the .358 Winchester. What was the idea? Just to slightly improve on the 35 Remington and hope the 35 caliber crowd adopted it because of the familiar 35 caliber bullet weights?
With proper bullet selection, I've always scratched my head as the generations of sages of the gun magazines lectured the acolyte class that the .358 Winchester was a nice "brush rifle", but that's about it.
