The United States has never ever chosen a cartridge because it simply maims. The whole "wound one, incapacitate 3" idea is nothing but a myth.
One thing the 30-06 gave the infantryman was less dependence on artillery & crew served weapons. It had the capability to reach out to longer ranges when needed and has superior cover penetration. In WWII those advantages were put to use to great affect. Going to a lighter caliber like the .276 would have meant a greater dependence on support weapons. TANSTAAFL. To get one thing, you have to give up another.
I have to disagree that the Garand was the last time the US infantryman clearly had the superior weapon. There's no denying the AK works. But the M14 and M16 family of weapons still give our soldiers & Marines an advantage. The Marine Corps in particular used M14s to great affect and by all accounts, most hated having to switch to the M16.
I know the debate of the reliability of the M16 FOW vs the AK still rages. But when you strip away all the smoke and thunder, we're left with the fact that the M16 FOW is a highly refined design that is very reliable, very durable, very consistent performer from rifle to rifle and pound for pound deals with heat better than any other design. It also has the advantage of being the easiest rifle to operate. It's also easier to add "force multipliers" to, such as red dot sights, than the AK.
If we had adopted the .276 Pedersen, it would have changed our tactics. We would have had a round with less penetration chambered in the Garand. We would have had a rifle that was unwieldy for close combat with less penetration. Soldiers would have been more dependent on other support weapons. It may have forced the US to develop a smaller infantry rifle with greater capacity sooner, requiring the introduction of another FOWs during the heat of combat. It would have placed a greater strain on communication technology.
The fallout of adopting the 30-06 leads to the adoption of the 7.62x51 and the 5.56x45. The 7.62x51 carries on the legacy of the '06 by giving the US the capability of greater range and penetration in our support weapons. The 5.56 gives us a round that's more controllable, is much lighter, is lethal, is fired from a much lighter weapon and is inherently accurate.
Yes, the adoption of the .276 Pedersen would have changed things- tactics, weapon's development- but it may not have been for the better. The .276 would likely have better cover penetration that the 5.56, it also would be less than the 7.62x51. It would shift the reliance on support weapons up one level. We can't say for sure that would be good or bad, but it would be different. In any case, the adoption of the '06 has left us with the legacy of three great calibers (four, if you count the '06 itself)- the 5.56x45, the 7.62x51 and the .50 BMG