If you're not using the bones and connective tissue in good alignment with the ground, how is it that you are not using more muscle to resist the force??
Obviously if you use structure you have to use muscles to hold yourself up.
I believe you are familiar that you can use the muscles of the legs to push back while maintianing structure, and thus you should understand that you can use non local muscle to generate power conveyed by support structures of some kind to the point of contact with the opponent. (I don't consider this to be internal, just showing that this builds upon the initial logic you have presented).
Chris, let me know if the following is accurate in terms of your opinion:
So strictly speaking, by your definition, using musculature elsewhere in the body which conveys a force via support structures is less efficient than using structure. I would agree if the only judging criteria is the amount of muscle applied. The problem is that structure is limiting, its effectiveness drops when your posture is compromised in which case, the average person has to rely on more muscle to deal with incoming force. If you can use the body in the manner I am talking about, you wind up using far far far less muscle when the structure is compromised.
I don't think anyone is going to argue that you never want to give up structure, just that you learn how to use other manners of movement, it will not only enhance how you use structure, but not leave you vulnerable (like the typical person is) when it is compromised.