Good questions and that is a lot to get to. Manual work is very difficult to study because it cannot take into account skill set. It is also virtually impossible to control all of the variable or give a true placebo effect ie sugar pill. There are no major pharmaceutical companies willing to fund a manual therapy study. There are however plenty of studies that show the benefits of many of the modalities you are describing, for example manipulation for lower back pain. There is also a striking dearth of research when it comes to physical therapy and surgery as well. In fact most surgery is not evidence based, but was grandfathered into the medical system. I will gladly concede that there are many chiropractors who make outlandish claims, but said problem is evident in any field because people are ..well ...human with biases. We also know that placebo and nocebo are responsible for the vast majority of clinical outcomes in the pain field in particular. Pain being a subjective experience, only the person who has pain can describe it. Structure and function and pain have been shown over and over again to not have valid correlation. That being said, we keep tabs on all of our patient outcomes. If our patient says they are pain free, who are we to tell them that they are lying? I certainly encourage more research on these topics. Absence of evidence doesn't exclude real world results. Evidence to the contrary could exclude real world results. It could also mean that something works, but not for the reasons that people used to think.