I agree. The thing that seems to be twisted about it is that I do not remember seeing any of my school teachers (professionals) in the restrooms cleaning the toilets or mopping floors.
It still happens in the professional ranks, but it is a bit more subtle, and it is just as wrong.
In teaching, the new teacher is assigned to the classes that none of the veteran teachers in the department want to teach. IMO, that is the primary reason that 9th grade in the U.S. has such high failure rates--that is where most of the most inexperienced teachers are slotted, and they don't have the skill to deal with the problems of students of that age. That is, also IMO, the reason so many young teachers quit after only a few years in the profession. When I was a department chair, I made sure that did not happen, but that is not the norm, believe me.
I have several relatives and friends who are nurses. One graduated at the very top of her class and was immediately hired by a hospital where she was ground into submission by the same process. The veterans got the cake assignments while she was nearly killed by her schedule. She quit and happily took a much lower-paying job in a private office. In contrast, another of my relatives was employed by a hospital with a humane policy that made for a happy employee who wanted to excel in her work.
When highly motivated people (teachers, nurses, and DMs) feel that they are being exploited, their motivation is destroyed. They work with less care and enthusiasm, and they look for a way out. An unthinking operator will exploit DMs because--well, that's the way it happened to them, I guess. A wise OP will carefully nurture DMs so that they will provide customers with excellent service and, hopefully, go on to be caring and skilled instuctors.