This is true. A PhD is very close to an apprenticeship model: study at the feet of an expert doing simple work, prove your competence (master's degree/prelims)

This is true. A PhD is very close to an apprenticeship model: study at the feet of an expert doing simple work, prove your competence (master's degree/prelims) to start working on your own account under supervision, finally submit masterwork (PhD thesis) to be counted as an expert yourself.