As I understand, scapular winging may be caused by tight pecs major/minor and weak mid-lower traps and rhomboids which is common in TOS.
The weak upper back muscles are overworked and overstretched which causes pain.

The longer we have bad posture the more severe the problem gets. After a while the muscles can't cope with this anymore, develop spasms and trigger points and hurt all the time.

From my experience, it takes very little to send the sick muscle into spasm and very long for it to recover. The bad posture can't resolve overnight and may require many months of PT.

Upper back pain may or may not be a TOS symptom. Dorsal Scapular Nerve (innervating rhomboids) can be entrapped in the scalenes and Spinal Accessory Nerve (which innervates the traps) can get entrapped in SCM. But it may be that those muscles are not to blame.
TOS surgery may help in case of scalene entrapment, but probably not in other cases. E.g. if pain is from trigger points due to overstretching then the surgery won't help.