If a cartridge trajectory or flatness doesn't matter, what would you look for in a rifle?

I can't help but think, lighter and more accurate the better? within reason of course, I don't need a 3lbs rifle.

My point is if you know your bullets trajectory and have an accurate range finder, who cares how much your bullet drops etc... as long as it's got enough energy to get the job done on the game at hand?

I'm thinking of a western/mountain rifle, possibly 270win vs. 308win.

I'm thinking it would be easier to build a lightweight .308 than .270, can get away with a shorter barrel on the .308

also a short action, lighter, stiffer/stronger than a longer 270win.

Am I missing something on why to shoot a 270 over a .308? aside from flatness of trajectory?