I will add my anecdotal perspective as a rheumatologist at a tertiary care centre to your second last reference. I have a lot of respect for the work my NP/PA colleagues do, particularly on the ward. Yet I see a notable difference in the quality of referrals from MDs vs. most NPs/PAs whether it be from clinic, ER, or ward. With some exception it's often please see for [subjective complaint], a + random test that was checked, and query [disease that goes with that antibody] or a misunderstanding of what I see in my discipline. Not to say that MDs have it perfect but I'm not sure if it's the shorter training, more algorithmic focus, less confidence in their physical exam that drives this. As a healthy 20 year old I'd have said an NP/PA is great for primary care but I just don't see it as a solution as people age and get more medically complicated.