For whatever it’s worth, your best answers will probably be forthcoming from people who understand psychology’s unique language, and the how and why of that language’s application. Again, for what it’s worth, musicians themselves reverse that language in common usage (or more to the point, apply the common usage), e.g. the principal ‘cellist of the Spokane Symphony, or the Seattle Symphony is an expert; Yo-Yo Ma is a master. The principal of the Cleveland Orchestra is somewhere in between. Going further, audition classes with the highest-level touring concert artists are universally called "master classes." The older teachers that are held in the best regard, the teacher’s teachers that professionals travel to for coaching, are called "master teachers."
None of this to say that the way psychomotor learning uses the terms is wrong, but all that to say that it is very specialized—not that you don’t already understand that better than most.
Additionally, the current benchmark for musicians is now seen as more like 30k hours—but they have to be goal-directed.
Again, FWIW. I understand that in learning outcomes, a student can demonstrate "mastery" of a subject, say, writing a press release, or the basics of playing a c scale harmonized in thirds, and that hardly makes them an expert in the field.
We are indeed talking about two very different language conventions. I say this as a full-time pro musician who’s first degree program was psych.
I realize that this post isn’t helpful for you in any way, but it might be helpful for the discussion.