I see where you are coming from. Nowadays, it seems like information travels so fast, it is exceeding our thinking speed!
On the other hand, when making a cartridge decision, you are often a person with a purpose/want/need/situation which doesn't quite match some old cartridge perfectly.
i.e. 308 is a great deer cartridge, but 338 Federal is so cool and you might use it's extra umph on an Elk, so guys get 338 Federal. Or 308 is good, but 300 Lazzeroni is like a missle.
So, hype kind of outweighs good thinking.
All this said, I often recommend both of these rounds, DI AR's, fixed power scopes, practice and other non-cool things. I recommend 308 because:
- Rifle makers are matching ammo size and vice versa better
- 308 has the most loads available of any round. You will be able to find factory ammo which shoots lights out in your gun!
- When you are on your dream elk hunt and you find out you left your ammo at home, you can buy 308 Win at most stores in like Gardner MT on opening day! Not true for 300 super duper mag. Heck, they would likely have your load in stock and more than 1 box. I have done this with 30'06 before. I was 13, I think. The think which struck me was they only had 30'06, 308 and maybe 30-30! My dad was shooting 7 mag. I told him I was glad we remembered his ammo!
- In 20 years, there will still be 308 ammo and 30'06 ammo available. Something like 300 WSM maybe as sparse as 264 Win Mag is today.
- Also, there are alot of people who know how to make 308 handloads work for every gun. Not as much data and know how for 300 Lazzeroni or 375 Jones Rhino Stomper.
Along with this, why aren't we rejuvenating the greats like 22-250 with a 1:8 twist, 7x57, 257 Roberts, 7mm-08, 6mm PPC(as a varmint round), 35 Whelen, 358 Winchester, etc.
Why invent so many new rounds? I think it often is a way to get better case designs, higher pressures and modern throating ideas into rifle without having a dangerous Hi/Lo powered ammo issue like we have with 45 Colt or 223/5.56. Isn't 5.56 really a 62,500psi round, but 223 Rem is a 55,000psi round?