The "Darwinian struggle" argument is fallacious, as the status quo is not necessarily the best way of doing things, especially in a conservative, class-based society like the military. History is full of examples of how the generals (ultimate expression of.the officer class) got it wrong.
With all respect, there isn`t any NEED for officers and a two-track military. This is 100% a holdover from the European class system. Just think about the expression, "an officer and a gentleman." What do you think GENTLEMAN means -- someone who is polite? The distinction between "officer" and "man" is entirely historically based--and ridiculous. Like lawyers using the designation "esquire"!