We can work backwards from your findings. “Left deltoid and bicep have increased polyphasic potentials” means the C5 and C6 roots are involved. “Left tricep shows the same plus reduced recruitment” means the C7 root is involved. Your MRI notes “left paracentral disc herniation indenting upon the ventral thecal sac and flattening the left hemicord”. This can affect the motor nerve on the left at C5-6 (which would be the C6 nerve root). Other level have no root compression. Why you would have C5, C6 and C7 root involvement with a compression only at C5-6 does not fit. I would look to causes other than the disc herniation for the disorder. You can try a selective nerve root block at left C5-6 for symptom relief. If that gives you temporary relief, a surgery might be helpful for a portion of your symptoms.