If you were lucky enough to own a helicopter, would you take it to the local garage for a service as opposed to a helicopter specialist? Given the complexity and the consequences of the job not being done properly my guess is the answer would be no. Similarly I am not sure I would eat Fugu Sushi prepared by my local fish and chip shop rather than one of the very few suitably experienced sushi chefs.
In both the above examples the two pairs of ‘practitioners’ could legitimately be described similarly, in the first instance both could be termed mechanics and in the second both could be described as specialist fish chefs. These general descriptions whilst perfectly correct do not describe the specific competence of each.
A helicopter mechanic and car mechanic will share much of the same knowledge, and with this shared knowledge a car mechanic could probably read up about helicopters and make a pretty good attempt at servicing the helicopter however without the experience and practice within the speciality would never be able to do as good a job as the helicopter mechanic. Reading and theoretical knowledge will only get you so far, fault diagnosis and working out the fix is more often than not about intricate knowledge and experience. Mechanics will tell you that identifying a problem is often about what they can hear and what they can feel.
Independent nurse and Pharmacist prescribers can in theory assess any patient and then prescribe almost any product. However there is a huge caveat to this within the regulations and that is that they can only do this ‘within their competence’. I think you can see where the above analogies are going, just because a nurse or pharmacist prescriber has read up about a particular condition or treatment does not to my mind make them competent.