With all due respect, I think you might be conflating being a floor or staff nurse/RN with being an advanced practice nurse like an NP, CNM, or CRNA. Mel is a CNM. Most NPs and CNMs wear business casual often with a lab coat in office and clinic and often for rounding in hospital and will wear scrubs for medical procedures or deliveries.
Doc defers to Mel on diagnosis because he is a general practitioner/family practice doc and she is a specialized field in nurse-midwifery who up until recently worked at a high-ranked, high-volume, high-acuity hospital and likely has more obstetrical experience than him as well as more experience with unusual cases. While Doc, as a FP doc, does attend a few of the low-risk births in town from locals, he is unlikely to be intimately familiar with all the unusual complications and issues one would see at a big hospital and he is also unlikely to be up-to-date on new medical treatments and research specifically for OBGYN stuff. Mel has to keep up with that for her job and has probably seen far more women with issues like Hyperemesis Gravidarum and tried different treatments with them. Actually, even before I was an advanced-practice nurse myself, I worked closely with a doctor who consulted me often even though we were in the same specialized field AND he had worked in it for 20+ years. We would brainstorm treatment options/plans and this was because he respected me as his intellectual equal (as Doc seem to with Mel now) and he recognized I brought a different perspective both from being at the bedside and because I had extensive history as an ICU nurse prior to working in women's health with him and so was more familiar with some of the non-gynecological emergencies and how they would be treated in the ICU.
I actually think this show is one of the *most* realistic depictions I have seen of a doctor-nurse or doctor-NP relationship and how they work together as part of a multidisciplinary care team. I was shocked by how accurate it can be on that note. Nurses do not work for the doctor (their supervisors would continue to be nursing leadership) and particularly in a field like advanced practice nursing, you are fairly autonomous and independent while for certain fields and in certain states you may be supervised by a physician signing off. I cannot tell you how many times even as a baby nurse, physicians would ask what I thought we should do when they were stuck. We each bring different things to the table and Doc recognizes that and uses Mel's strengths and experience to fill in the areas where his knowledge may not be as deep.
As for Preacher, I don't know, maybe they want us to believe he is a saint. Maybe we're supposed to think he is deeply in love with Paige even though he never got to really act on it and would thus do anything to keep her safe.
