And I'll add that with sufficient horsepower behind them and an appropriately constructed projectile, bigger bullets hitting harder offer more options for acceptable fast killing shot placement. If your shooting a deer in the head from 5 feet away then sure, it doesn't mean squat if your using a .22 hornet or a 460 weatherby. If your taking a hard quartering shot through a major joint a bigger bullet inspires confidence and is more dependable. If your hunting things that can hunt you back, and have no guarantee that you'll be offered up an opportunity for absolutely perfect shot placement, especially if one does decide to come at you, then all that "shot placement is all that matters" goes right out the window.
If everything goes exactly right for sure the 6.5 creed is a grizzly rifle and much more…
I find it unwise to go into any kind of hunt expecting, planning, and making my success contingent upon everything going exactly right for me. When things go less than right as Murphy would have them do, overkill beats the alternative.