An MD is the first degree one earns in the subject. It takes four years to earn. It used to be a bachelor's degree: MB or MBBS. In the modern era, the premed requirements pushing total medical education to five and a half years probably justifies making the degree a master's degree. The residencies and fellowships that physicians do after earning the MD that are virtually required for any physician to practice probably make calling physicians "doctor" appropriate.

Still, calling the MD a doctorate is questionable.