The only problem with this is that "classical" warfare is pretty much dead. Asymmetric warfare is the fighting style of the future, and of the present. Do you see massive armies duking it out on the battlefield today? No. And that's because massive armies are unwieldy, and a pain to support economically. Guerrilla fighters are easier to support, and can last forever, eventually winning their war because the "classical" army's public will eventually grow tired of constant war, even though they could easily win.
That's what you're missing in your assessment. Public opinion. In a modern democracy (which is to say, pretty much every major power on earth minus China), public opinion reigns supreme. Which explains the Vietnam effect: the US had better training, better weapons, better tactics, and inflicted something like a 10-to-1 casualty ratio on the VC forces, but they ultimately lost the war because their public grew tired of it. War weariness is not to be underestimated, and it is foolish to think that the public will infinitely support more and more of their sons and daughters being drafted into the ranks of a "classical" army.
The difference between the two is that guerrilla tactics rely wholly on the implicit support of the public. It can prove impossible to successfully occupy a nation if the citizens are always non-cooperative and fighting back, supporting the defense/resistance movement. Guerrilla tactics are employed because a small, harrying force (like the commandos you mentioned above) can easily disrupt the massive supply lines and support networks needed for the "classical" army's power, and inflict enough casualties to make their public war-weary. You cannot understand asymmetric warfare if you look at in from a symmetric viewpoint, which is what you seem to be doing. In a stand up fight-- that is to say if the classical army managed to corner the guerrillas-- of course the classical army would win! But, here's the catch. Do you remember the American revolution? Yes? Who had the classical army there, with 25% more power? That's correct, the British did. But, because the United States used guerrilla tactics, not to mention receiving help from a sympathetic power and refusing to come into a stand-up battle with massive British forces, the Americans eventually won. By all odds, this victory should have been impossible, but it was not.
So, while I understand why you'd think that the classical army would always win, on home terrain (something you didn't specify in your question, whether we were attacking or defending) the guerrillas have the advantage. If you'd like, I can cite some official sources (from the Pentagon's official warfighting strategy, no less!) that confirm this.