I am licensed as a prescribing/medical psychologist and have never practiced as such because there's no benefit for me. IMO, it's stupid to be concerned about this. I do believe that if psychiatry was really concerned about this, practitioners should hire medical/prescribing psychologists as another source of midlevels for both safety and profit
Practice: In RxP states, psychologists can only prescribe after a physician has approved the script. Yeah, not even close to the same level of independence of NPs and PAs, state depending. What's the significant difference from this practice and that of other states? I can see a patient and recommend a medication in pretty much any state in the nation. Physicians can call me an idiot and say no in any state in the nation. So what's the benefit?
Money: IMO, money is not substantially better unless we are talking about cash based practice. With insurance, say your practice is mostly comprised of 99213. So around $200-300/hr if your productivity is 100%. In neuropsych, I can make at least that using technicians without being face to face with patients if I wanted. There are other cash based practice areas which are as or more lucrative than prescribing (e.g., psychoanalysis, forensics, etc).
Demand: Demand is much higher for prescribing/medical psychologists. While this may drive the increased money for psychologists, it means more work. IME, most of the demand comes from patients with crappy insurance. I don't know about anyone else, but I'd prefer to do high pay/low volume work rather than the converse. My analyst's 50 minute "hour" is higher in cost than four E/M codes.
Hassle: Frankly, prescribing looks like a hassle. If I see someone for a neuropsych assessment, no one is calling me at odd hours because they have had an adverse reaction to crap, or "lost" their scheduled stuff, or whatever. No one is calling me from a pharmacy about insurance stuff. If I do forensics, there's no surprise person in my waiting room or need for coverage when I want to go on vacation or get drunk.