I don't recall anyone saying that smaller cartridges are "better than" bigger cartridges.
Phil Shoemaker did note that smaller cartridges have indeed worked better, on average, for brown bears than larger cartridges. But he did NOT say that "almost anyone could shoot more accurately with them."
Dunno how many brown bear hunters Phil's outfitting company has guided, but over several decades it's been quite a few--and his clients regularly take very big bears.
Might also note that Phil has used a wide variety of cartridges to back up brown bear hunters, from the .30-06 to the .505 Gibbs. He still prefers his .458 Winchester, but that's for stopping charging, wounded bears, something very different than hunting unwounded bears.
Nor do I recall anyone saying that smaller cartridges are better than bigger cartridges. My statement was to the "impression someone might get". And, of course, we know about the native girl (Stent) who killed a record book grizzly with her single shot .22 Long cartridge. And I know my oldest son killed dozens of warthog in Africa with his single-shot .22 LR with brain shots for protein. He even literally "flattened" a wild cow with his single-shot .22 LR, that was a real problem in the village, with a 40g between the eyes. And so on. So I'm aware that anything, except a 30-ft shark or huge whale, on land can be killed with minimal cartridges firing an appropriate bullet into "the right" spot. As we all know, I hope, killing is one thing and stopping is another. My statement was limited to black bruins being "flattened" (DRT) without a CNS hit in using appropriate bullets in .458", whereas I've killed several using medium calibers that went some distance after the shot that were not hit in spine or brain. They were dead but not DRT. Where I hunt that can make a difference.
All that to make a single point, really: most anyone can learn to shoot a big-bore rifle with accuracy, without denying that most land mammal can be "killed" with about any rifle cartridge, and... I've written that a person with a .308 Win rifle "needs" nothing more for all N.A. hunting - or its equivalent. But killing is one thing, stopping is another!
