Hope, not all PN's improve with time. Many of us have prevented progression, and in my case I did improve (but not 100%). For most of us, once you have PN you have it always.
But the severe, pain, sweating, discoloration, and other things RSDers endure, we don't have that. When things get really advanced in PN we become numb as a rule. (also weakness, and disability follow). Some become paralyzed in a way.

The genetic ones like Charcot Marie Tooth, (which has many variants) don't have studies showing nutrients help yet.

Some of the autoimmune ones are connected to gluten intolerance.

There are over 100 forms of PN, but many are linked to low levels of some nutrients. And the nutrients that help mitochondria, like carnitine and CoQ-10 may help those that have mitochondrial damage like arise from chemo or HIV treatments.

The problems with PN are that finding the culprit can be difficult and many doctors, don't bother. Without a hint as to what is wrong, then the proper treatments cannot be applied.

There is a new test for sensory neuropathy, and that involves a skin biopsy to count the nerve endings actually present. EMGs don't as a rule show small fiber sensory changes. EMGs do show motor (muscle) involvements, typically called axonal.

When I read here on RSD forum I am struck by the similarites too that exist between the two disorders. But they are different also in alot of ways.