Even if we had more licensed physicians we would still have a large number of staff per doctor. A radiologist might be able to administer contrast to a patient, check their vital signs, transport them to the MRI machine, and run the scan but that's not a good use of a radiologist's time. Better to have nurses, orderlies, and technicians do all that so the radiologist can focus on reading the images.

Yes, it's obvious that some level of support staff are a good idea.

Now make an argument that the current arrangement is more optimal than the one we might end up with if there were more doctors.

That part is obvious. Regardless of the number of physicians, they will always be the most expensive resources. Thus any procedure which can safely and legally be performed by less expensive resources, should be.

That is scarcity thinking.

Yes resources will always be scarce and we need to manage accordingly. That is reality.