Right, which is why flat-nosed bullets designed for lever action rifles are softer than spitzers, so that they won't pencil through at lower impact velocities.
And yes, so long as the bullet is an appropriate cup/core or partition type, there isn't much difference on game when shot at under 200 yards between a .300 WM, .30-06, and .308 Win for that matter, everything else being equal. Get much past 200 yards though, and the differences are evinced.
With the monolithics that are so in vogue now, velocity is much more critical for expansion. From my observations over the past decade or so of posts on this and other hunting boards, I think a lot of hunters are wasting money and actually diminishing their chances of a clean kill by using TSX and similar bullets on deer-sized game, particularly in calibers under .308".
That being said, my favorite coyote bullet is a 90 grain old school X bullet out of my .243 Win. It pencils through without tearing up the pelt, yet still drops them in their tracks.
