Ballistic coefficient has favored 6.5 bullets for a while. My garand weighs in at about nine pounds or more. Clip capacity 8. 6.5 Grendel about 7 pounds. 20 round 5.56 clip holds 16 with the right follower. Muzzle velocity is about the same. Bullet weight .30 cal. 168 grain 6.5 123 grain. Honestly I don t know what’s the best. Going back won’t work and changing all 5.56 rifle barrels and bolts and clips seems prohibitive. Then the supply of ammo to any new round. This whole issue is a bear that I am glad I don’t have to wrestle with.
There are no free lunches because of the physics involved, and no one cartridge will be able to "do it all." Heck, I have tried to find the "one gun" solution all my life, and I can't do it even with my limited set of parameters.