I am fused C4-7. It was done over two surgeries and after the first I went two years with it broken and causing damage to everything else. That being said what had happened was my body ended up "guarding" the injured parts and I used/over used parts of my body that didn't hurt. I had the surgery and I had no prior problems in my arms or hands other than the shooting pain from the nerve compression. I now have total weakness, grip, and pain like you describe, although not as severe.
I started with a new set of doctors and they have been running me through the mill again trying to figure things out and I now have torn rotator cuffs, and carpel tunnel on both sides. I thought this was an interesting finding as I NEVER had that before and the way the doc told me just today was how I explained it. I trust him because he is my PCP and has no affiliation with the surgeon. He says, and the surgeon and neurologist also agree, that my rotator cuff injuries were more than likely old from the wreck and caused from the high impact and seat belt useage. He said I probably didn't feel the effects of those before because your body minds what hurts worse.
Going on that logic if you were using your right hand to compensate for your left hand, then it may be very possible to have developed severe carpel tunnel syndrome, which can cause your symptoms. You may not have felt it before because of the pain elsewhere and now that is what the primary source of pain is.
I will tell you this, the surgeon is going to distance himself from you as fast as he can now. You need to move quickly to get an EMG (Nerve conductance test) to rule out Carpel tunnel or any other form of nerve compression or damage. Your PCP can refer you out for that. When you get those results you can arm yourself with knowledge and attack it from there and possibly get corrective treatment from the surgeon if indeed it was their fault.
I wish you the best and RANT away that is what this is here for and there are a lot of us in the same sinking ship lol