Yes, and the medical licensing board is in charge of that, not the employer, and every doctor is evaluated to the same standards. Also, doctors are only one of the professions mentioned.

Somehow in programming every interview starts from the assumption that the candidate must prove competence to the employer, and the employer decides what "competent" means.

Yes but not for a specific job, given by the employer, and certainly not for every job. And this is only one of the professional fields mentioned.