The issue is (in cases like mine) there is no way to prove what is causing the compression. The clinician organising the surgery was making a "best guess". Apparently the area where the nerves/arteries are was incredible small (3mm) which led him to "guess" that the area was easier to compress with an abnormal muscle growth.

But nobody could see it or prove it. The only proof was that the physio exercises didn't work and the scalene block provided relief.

In my opinion the physios are far too dainty. I am a fully grown man. The stretches and flexibility exercises are great for pain management. But to strengthen muscles you need to tear them and regrow them over and over. They give me a long elastic band to do seated rows and it's just not enough resistance to actually build strength.

And the surgery, in my case, should be on the upper back to pull the shoulder back down. Not cutting parts of my ribs out. Xray showed no rib abnormalities whatsoever. If you do, then yes you probably need them removed. But this cookie cutter approach just seems irresponsible, considering the risks.

Oh and I haven't received an answer to the original question. I'm pretty sure if scar tissue was growing into the nerves then it would be pretty hard for the Botox to do its job though...

Many with TOS got worse with cookie cutter PT, the stretchy bands , building the wrong muscles.. Stopping repetitive /straining activities may benefit more and adding flexible movements , gentle stretching.
If all your right side is affected.. check your shoulders, hips, knees do they look level with the other side?
If uneven, you might look into nucca /upper C spine adjusting..
Some info - Up C Spine

Some with internal scarring post op tried many things for pain with little results..

It's not droopy as in I was born with it. In fact at times you can barely tell its lower than the other side. I was working at a factory and they had me on the same job for months on end. Before that, looking at my medical history, there was absolutely nothing.

The leg pain, it seems, is from the right scapula being pulled out of position by the weight of the shoulder and over stretching the muscles/nerves in the lower back.

I did have an MRI on cspine which showed nothing. But when I put on the brace, I realised the lower shoulder was making me face slightly to the left. It was really weird and disorientating to face straight in front of me for the first time in 5 years. Really messed with my balance.

Could also contribute to leg pain, having spine slightly out of position for so long. I would like to see a chiropractor, just to have my posture analysed.

And thank you for the inspiration. I've had so many clinicians tell me it will be permanent so I'm not too optimistic it will be cured. "Able to cope" is what I'm aiming for...

Were you born with your droopy shoulder?

Some can be born with unevenness, or you can get it from accidents or even pain or postures making you carry your body differently..
Head/shoulder hits or falls may cause c1-c2 misalignment.. can throw the whole body out down the line..
I had a concussion as a teenager- got bucked off horse & hit my head..so that might be a factor for me..minor car accidents, sports ...

uneven body alignment - Google Search

My right shoulder was droopy. It is much better now but it will get lazy at times. It is as much a strength issue as it is a neuromuscular issue. You must constantly keep it at the correct height consciously until it learns to unconsciously stay there. Meanwhile supplementing with strengthening of the upper trapezius and levator will help as well. Best of luck. In my case strengthening the neck and shoulder elevators and upward rotators has helped me tremendously.