Let's start by saying that I have no personal beef with the 308 having built more custom rifles and owned more rifles in this cartridge then ALL my other projects combined.
So why is the 308 so popular??? Because it is a NATO cartridge and the US loves their 30cals. With the enormous number of shooters that MUST use this cartridge for work, it makes sense that they would also use it for play.
The cartridge that must be used in Palma and service rifle (until fairly recently) shooting and a great hunting cartridge, it has extremely wide appeal.
However, ballistically for LR, it is definitely in the lower half of available choices. It is a small case so does not have the horsepower to get high BC bullets to velocities that matter. Even at BR pressures, a 308 will never launch a 210/220/240gr bullet to any velocity worth mentioning.
Ballistics are determined by the shape of the bullet (its BC or drag) and the muzzle velocity. Bullet weight has precious little to do with performance however, heavier bullets in any calibre tend to have higher BC (more material to make longer streamlined bullets).
Bullet with the same BC AND drag function launched at the same muzzle velocity will have the SAME ballistics despite having very different weights.
If competing, the 308 may be dictated by rules so have at it. It does work. However, if building a LR rifle for pure performance, there are many many better choices is calibres from 22 to 7mm. I have left out the big magnum 30's and 338's as this is not the place to start.
LR choice will always be determined by available bullets. For a while, service rifles were shot with 223 and 308 with both doing about the same. Now, you will have to look long and hard to find any 308 service rifle competing with the new gen 223 AR's. The difference in performance is so drastic, a 308 only class has been started so old iron will not go to waste.
The wealth of components and info is not limited to the 308. Every caliber save the 25 and 270 have an abundance of awesome bullet choices. Even the 25 and 270 have great bullets just not many. Not sure why as they can make fantastic shooters. We will just have to wait for bullet manf. like Wildcat bullets to change the landscape.
For now, LR light rifle is dominated by the 6.5. The 6mm is making strong headways and if more 'better' bullets become available, WILL take over from the 6.5. In the heavy classes, the 7mm is making strong inroads into what has been a 30/338 dominated class. Better bullets just make that possible.
As I have recommended many times, the best starter cartridge is a fast twist 223. The Savage FV being the least expensive shooter! From there, the world is your oyster. There really is no wrong answer. It all depends on your uses and rifle parameters.
We have such a huge range of choices, the 308 is like Vanilla at B&R's. Still a good choice but....
Jerry