I had a patient that had surgery for Sprengel´s deformity some years ago but I do not think that the doctor that performed the surgery are here on research gate. However if I remember right she was about 3-4 years of age at time for surgery (maybe younger but not older).
In my opinion the problem lies in the engagement of the spine on the one hand, and the extent of restricted abduction of the upper extremity on the affected side. In some cases there is a hard bond between the scapula and the spine - the so-called os omovertebrale.
We usually subject children with Sprengel's deformity to regular control examinations and x-rays (over 6 months). Meanwhile, a systematic physical therapy is carried out. If a secondary scoliosis emerges and the ROM is not improved with the elapse of time, then surgical correction is indicated. Usually, this happens at the age of 3-4. So here our opinions coincide entirely.