I have been tossing some ideas around in my head. Please comment.

What are the claimed modes of action of these approaches?

Hard bracing, I take it, is supposed to immobilize the spine in a straighter configuration. I assume this means that the growth on the side that increases the curve is arrested through pressure and the growth on the side that has to grow to straighten the spine is allowed to go on unimpeded. It is not claimed to do anything positive with muscling w.r.t. correcting the curve. Indeed, if hard bracing immobilizes the spine in a particular configuration, then it is also immobilizing the muscles.

Soft bracing like Spinecor is supposed to allow more mobility and flexibility while simultaneously either holding a curve or maybe decreasing it. If it is to do that then it must hold the spine in a configuration such that the growth occurs where wanted and no growth occurs elsewhere, as for hard braces. Now I don't know if that goal involves changing musculature or not. But bracing, hard or soft, takes over for certain muscles and there will be atrophy. Bracing can't build up muscles. If Spinecor allows for movement such that abnormal growth is not prevented, I'm not sure how it can succeed.

Which brings us to PT. At base, the claims of PT approaches necessarily are that certain muscles have to be built up to counter the curves. But what is the evidence that a lack of muscle caused the curve or that building up certain muscle can ever improve a curve? I don't know about other forms of scoliosis but idiopathic scoliosis is a result of uneven growth of the vertebrae as far as I know. Why would PT ever be thought to be able to address that? And it seems the perfect vacuum of evidence for the efficacy of PT approaches bears out this thought.

In sum, if idiopathic scoliosis is caused by abnormal growth patterns of the spine, how can any approach that doesn't try to arrest those patterns ever going to succeed? And the corollary, how can any approach addressing musculature ever hope to succeed?

Fire away!