That's part of Diamond's point: These societies are organized on a small scale. Other similar societies scaled up and moved to a chieftain system.

But in any case, even small, elite, independent army units have the usual officer/enlisted dichotomy, even if in the elite units this is a less clear distinction.

Possibly, if the line of this post is correct and I am not taking it too far, this is because the SEALS, Sayeret, etc are implicitly expected to be agenty in a way that most soldiers are not.