it does also take an actor to sell the vision of a character. an unconvincing portrayal would make the vision seem more like a farce or caricature and if anything undermines the morals
The original Janeway for Star Trek Voyager only filmed like one episode and her take was very different (French actress I think. And maybe they were aiming for a Picard analog).
It’s true, and Stewart was a great actor. But he would have sold a vision of a morally compromised captain just as well. The vision is Roddenberry’s.