Your statement sounds pseudocorrect but the underlying assumptions are that: a) we are currently able to diagnose all nosological entities efficiently, b) we know which treatments are working for each of said entities and c) all people react the same to the same medications, d) all medications that are indicated to treat a disorder are equal. Oh boy, wouldn't that be nice...
In reality you have an army of paper pushers that are hired and have their salaries paid to restrict what can be prescribed. For patients that fit well in proper diagnoses and are otherwise typical it is sometimes annoying but for the 1-2% of patient that rules do not apply (for so many reasons that I cannot possibly enumerate here) it is detrimental. The people who are actually doing this job are not happy with it, the doctors are not happy with it. Every step of the prior authorization process is designed to irritate the doctor or provider (like saying all the patients information again when the representative changes or not accepting the case id to pull out the patient information or "sorry Dr. we only accept this application by fax, we don't do this online" or "this patient's plan does not support peer review") and discourage him from doing it. I know patients that were turned away because their doctors didn't want to handle specific prior auths for them.
"But doctor why don't you want to prescribe medication A that is as effective as medication B but it has more side effects?" As your advocate, I feel obliged to recommend the best medication, if your insurance does not want to cover it then they should take the risk and the legal responsibility of their policy not force me to change my recommendation based on price. Of course, I will not start with the bazooka antibiotic for your tonsillitis but there is a medical reason for not doing that (resistance development). Right now, I have to spend extra time to even justify why a patient should stay on a good medication yearly even if it works great for them. The doctor is your medical scientist consultant, he shouldn't be burdened with saving money from the system, he will tell you what is best, if you want them to give you a value-for-money determination they can do that as well. If two medications work exactly the same, I would happily give the older and cheaper one - it has been longer in the market so it has been more extensively tested.