You're right, you don't have to supply a study. But on the same token, without one, you can't make an argument against the safety of DNPs.
I clicked on the first result when I typed in dnp curriculum on google, and they DO have to take pharmacology, pathophysiology, management of acute and chronic health problems, etc., so yes, you were cherry picking. Comparing it to an MPH is ridiculous, since it does consist of a good amount of clinical education. Is it enough? I, nor you know. I think you're losing sight of the fact that DNPs are not going to be getting plastic surgery residencies, or become dermatologists; they'll be in primary care.
One last thing: for all the talk of encroachment, I have never heard of any doctor, PCP or otherwise, struggling to find a job. CRNAs are trained and supervised by anesthesiologists; I don't think you can really call that encroachment. If CRNAs are able to do what anes does, but for cheaper, then they're a valuable commodity. In a restaurant, you don't need an executive chef to do all of the slicing and dicing, so you hire other people to do it. Is that encroachment, I think not.