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.
“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.” John Steinbeck
