Actually the skin punch biopsy does remove some small fiber peripheral nerves along with the epidural layers - "...Some of the available tools for testing have included the neuropathic pain inventory, quantitative sensory testing (QST), quantitative sudomotor axon reflex testing (QSART), electromyography, and nerve conduction studies. Additionally, another diagnostic technique that has recently become widely and commercially available is the skin punch biopsy, which is used to measure epidermal nerve fiber density (ENFD) ..." --- Routine use of punch biopsy to diagnose small fiber neuropathy in fibromyalgia patients: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4348533/.

Details of counting the small nerve fiber density from the same article -- "...To fill in the void of objective diagnostics for SFN, the skin bunch biopsy technique was developed at the Karolinska Institute and later standardized at the University of Minnesota and at Johns Hopkins University. These punch biopsies began to be included in the diagnostic workup of patients with suspected SFN after the identification of antibodies against protein gene product 9.5 (PGP 9.5). PGP 9.5 is a neuronal form of ubiquitin carboxyl-terminal hydrolase transported with the slow component of the axonal transport. The availability of this antibody enabled visualization of the extensive innervation of the epidermis [5, 14] and the capacity for quantitation of epidermal innervation by small fibers [9]. This skin biopsy test was so specialized, however, that it remained solely in research hands for many years. It requires skilled and highly trained pathologists to process the sample and perform the very detailed task of manually counting the nerve fibers. It has, however, recently become commercially available at many academic centers and a few specialized labs in the USA. Each lab has its own established cutoff values for ENFD (lab norms), which allow the practitioners to make a diagnosis of SFN with greater certainty [15]. The convenience and ease of modern day shipping methods have made this test readily available to clinicians all over the country...."

Even though it's only the size of a pencil eraser, my symptoms along with my physical exam and nerve conduction tests are enough for me. Why? Because I know even with the results of the skin punch biopsy, it's not going to tell me what caused my idiopathic SFPN. The only thing it's going to do is remove a few more of my small fiber nerves that are good for the sake of measuring the epidermal nerve fiber density.

It might be different if I didn't already have a diagnosis and I was still trying to find out why I'm having these numbness symptoms. Then I might be OK with having the neurologist order a skin punch biopsy if it would provide a diagnosis.