Sure, a 6.5 creed will get you there, but how often will it get you right where you want to go? Every, EVERY outside influence will affect that little bullet significantly more than a 300gr 338 round. A few squirrels fart during that 1.6ish second time of flight and you're off target.
Granted, the wind challenge that comes with 1k plus shooting is part of the fun, but so is hitting smaller targets at longer distances more often than not. Not to mention, long range Hunters may have no problem getting on target at long range with the likes of a 260, 6.5 creed, but want to have enough energy to make a humane kill
To each his own. I love my 308 and just picked up my Krieger barreled savage chambered in 260. They are great for mid range shooting. But there's something to be said about how it feels to shoot a big bore magnum rifle and to make hit after hit easily at 1k plus with enough energy to really swing steel.