All of that is true and I agree with you 100%. BUT, if I was limited to a single rifle, it would be 30-06 or 308. With my 30-06, I can get saboted 22s that go 4050 fps, and I can get 220gr monolithic solids that go 2350 fps. And in my Remington 700, all loads give minute of deer accuracy out to about 500 yards if I do my part. Sure, it kicks harder for a given bullet weight, but its not like I shoot 100 rounds a session out of my 30-06.
So, the only thing I disagree with you on is which cartridge makes the better 1-gun battery. The 270 is a most excellent round, and truth be known, I generally shoot only 2 rounds out of my 30-06, but then, I have a significant collection of rifles In many other calibers.