Wow! Always good to see someone so interested in figuring things out! Of course, as you have found, it is difficult for people to figure these things our because of different approaches and skill levels of therapists as well as trying to clinically reason your own problem is difficult even for a therapist as it is very difficult to objectify yourself.
My thoughts while reading were:
- the initial incident years ago was likely just a strain
- the related atrophy, tingling and nerve sensitivity is hard to say why without seeing you along the journey obviously. Just know that is very common for shoulder function to decrease with any injury or pain around the shoulder girdle and nerve sensitivity is often seen too
- difficult to say what is going on in cervical spine without assessing
I would say that for all conditions we look to restore full ranges of motion and strength. Yes manual therapies like graston and self directed work like rolling etc has a part to play. But what makes the effect is working on movement. Start looking at things like can you hold a strict dead hang on a pull up bar, a solid plank and side plank for atleast a minute and then more dynamic things like pushups instead of bench press, handstands instead of military press, dips, rows etc.
Most importantly work on range of motion every day. Yoga has been around for thousands of years for a reason. It's the real deal. Take tissues to end ranges daily and look to progress positions. What is your melting heart position like (likely no good), can you hit a middle split with a side bend to open the ribs and side of the body etc etc.
There is no quick fix for anything, that is everyones problem. The body is remodelling every second of everyday until you die. It remodels according to the demands you impose upon it. 12 months of daily well directed range of motion and strength practice will remodel your body well and you are young enough to remodel well.
Just for reference there are 168 hours in a week. Say you saw a therapist for 30 mins for graston or had an "adjustment", there would be 167.5 hours left in the week.....now you should ponder what would impose more demands on the body to remodel.....