The Chief Engineer Derby was a Gene thing, that the Enterprise was supposed to be so advanced and automated as a vessel and piece of technology, it didn’t need to have a dedicated Chief Engineer. When Gene left the day to day running of the series, the writers basically decided the absence of a designated engineer in the cast was a handicap in the writing.
I can see how the Enterprise should have multiple doctors, in the same way that a hospital has several specialists, with the CMO acting as the division’s manager. But, y’know, that would mean multiple characters and actors to pay per episode, which wouldn’t be cost effective for the production budget.
I can see how the Enterprise should have multiple doctors, in the same way that a hospital has several specialists, with the CMO acting as the division’s manager. But, y’know, that would mean multiple characters and actors to pay per episode, which wouldn’t be cost effective for the production budget.