I actually dont disagree with that statement in a rifle cartridge. Noslers data proves that as well, as generally the loads with 95% case fill so the best accuracy potential. I always measure approximate fill to the bottom of the shoulder in a case, and in alot of cases that will get you 95% capacity, and get you pretty close to the best load depending on the powder.
But you start looking at pistol powders? Its pretty hard to get to even 75% case fill with some powders. I use alot of TiteGroup and CFE-Pistol. I wouldnt even attempt to hit 50% casefill with TG otherwise things will go boom. CFE-P, I think my highest casefill is a 185gr in my 45, and its a handful at about 75% case fill, and I wouldnt go any hotter because Im already pushing +P on it. Same thing with the 9mm 124 load I run with CFE-P.