Less volume in the vessel, equal loads, greater pressures I suspect along with slower burning powders specialty than we had when the STW was born.
Considering the long barrel life of the 300wm I'm unconvinced that longer necks actually have much effect on throat erosion.
I won't be shooting over 1,200yds so I'm not concerned with being able to load the next generation of even heavier/longer bullets. If I were shooting ELR I'd probably do something completely different and move up to the Cheytac 375.
I think what the .375Ruger case does for us though is give us a very economical solution for wildcatting hunting rounds from 6.5-338 and even to .350 if someone wants to.
The short fat cases just give you an efficiency/economy powder wise we can't get from the larger cases.
Oh, if I really want to fling'm long, I still have 3 300 Rum's that won't be going anywhere including a one of a kind 300 Rum Sharpshooter.