Hi Caveman, welcome to the forum.
I understand your doubts with regard to the motor symptoms. I assume that your pre existing neuropathy was entirely sensory. But I’ll bet that neuropathy didn’t start suddenly, nor did it proceed stepwise.
It’s a common mistake to blame everything on diabetes, but the key is listening properly to the history. What should take place is what would happen if you didn’t have diabetes, EMG studies (electromyography), and an MRI of the spine at the very least. You may well be right about the lumbar disc problem, but whatever - it needs further investigation. You may have to wait for that, it all depends on future progression to change your neurologist’s opinion. That’s the way of every neurological diagnosis. Neurologists almost always use the retrospectoscope in making diagnoses of motor neuropathy, mainly because that’s often the only way to do it.
My experience, as far as motor symptoms go, is the same as yours, but I have never had (and still don’t have) any sensory neuropathy, nor any pain. It’s taken around five years of progressing through using one stick, two sticks, two elbow crutches and now a wheelchair to get a diagnosis, but that’s the way of neurology. That’s just my story, of course, and interestingly includes a decision three years ago that it wasn’t the diabetes.