You are exactly correct. One intervention to a thyroid will change the entire biological organism. You don't have to also intervene in the lungs, heart, etc., just the thyroid. So too for any complex organization: person, family, and corporation. In other words, working with an individual, in the proper manner, can change a family. No rigid model based upon the limitations of our predecessors should confine the natural growth of the field of therapy.
Bob Dylan also said: "Your old road is rapidly agin', please get out of the new one if you can't lend a hand, for the times they are a changin'."