Not a gun writer, but I recall that the late Finn Aagard, who was a renowned gun writer, tabulated some statistics along this line and came to the same conclusion as the OP.
On an elephant hunt in Zim this past April, I shot an impala ram through the shoulders with a 500 grain Barnes monolithic solid from my .470. While mortally wounded, the animal ran about a hundred yards before it died. That same rifle (.470) and load instantly dropped a bull elephant in it's tracks a few years prior with a frontal brain shot.
IMO, a .270 Winchester loaded with a 130 grain Partition would have killed the impala much more quickly than the .470 did. However, the .270 would have had no effect on the elephant if employed in a frontal brain shot. The mass and bullet construction of the .470 solid was needed to punch through the approximately four feet of honeycombed skull bone to get to the elephant's brain.
As any carpenter will tell you, it is important to have the correct tool for the job and not all tools are created equal. Don't use a hammer where a screwdriver is required.
