Otherwise, it's pathological and dysfunctional. They must be knowledgeable and understand that eventually the mentee becomes a peer. The letting go part can be difficult, but at some point, the mentor has to stand back and let go. Within each of us is an ecology of self voices. We each have the capacity to birth a voice that is authentically one's own and that works within one's profession.
Mentors can be helpful in drawing forth that voice.
It's not about parroting. It's not social reproduction. Mentors need to nurture the multitude in all of us.