"We might as well claim that all cartridges based on a rimless bottleneck case with ~.474" rim diameter should be traced back to the 7x57 Mauser round as it's probably the first one of that ilk."
As has been noted here earlier, Winchester itself indicated that the .30-03 was the starting point for the .270 when it introduced the round in the mid 1920s, a fact (not a decades-later guess) mentioned in the gun publications of the day.
As I also noted earlier, Winchester's engineers and ballisticians had absolutely NO qualms about dipping into the "funky & unpopular" vault for inspiration for new rounds.
The .220 Swift was based on an abysmal flop of a cartridge called the .236 (6mm) Lee Navy, while the .348 Winchester took its case inspiration from the .50-110 Winchester.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.