The question comes into play when discussing FPA of mid-levesl, ie can mid-levels like NPs safely and appropriately address MH patients without supervision of physician. The reason the studies are relevant is because NPs have gained FPA in over half of the US because they have successfully argued to legislatures, repeatedly, that they provide equal care as physicians. If the argument was just about increasing numbers of NPs and access, then you can do that with supervising physicians. If you don't believe it's an issue in the real world, join PPP and look into the legislation being passed and the arguments made. You'd probably be shocked based on your post.
All that being said, I'm not really anti-midlevel or anti-NP. I think they can, can often do, play a very important role in our system when utilized appropriately. The problem I have is when the independent practice argument comes into play, which is really the core reason for NPs claiming equivalency irl. I'm not worried about job security or earnings and I agree that the doom and gloom related to this is overblown. However, we shouldn't act like these arguments aren't being made and used to further an agenda without real life consequences. There's plenty of examples, but the more obvious is the advent of companies like Cerebral.
At this point though, I think the ship has sailed and conducting these studies now is probably pointless as you're saying. They were needed 20 years ago before FPA was the norm in the majority of states. There's not point in trying to hold back the floodgates now, and like much of history meaningful change going forward will come from suffering, in this case the suffering of many patients d/t poor care. Which is unfortunately why I don't worry, because being someone who provides thoughtful and good care who can alleviate suffering from others doing harm through poor practice of medicine is something that decent psychiatrists will be able to do for a long time going forward.