I think having Lt. Rahda as a navigator who was (ostensibly) a woman of colour in “That Which Survives” was really significant. It was clearly an attempt to show greater diversity and demonstrate that a South Asian woman could be just as professionally competent as a man, and could be entrusted with an important role on the Enterprise.
Unfortunately, as often happened in TOS and other film and TV of the era, they didn’t cast a South Asian actress. Naomi Pollack, who played Rahda, is a Jewish-American woman. She also played one of the American Indians, in heavier brownface, in “The Paradise Syndrome”.
It’s important to note that this kind of casting misrepresents other cultures and also limits roles for actors of colour.
That said, I still think “That Which Survives” sent a strong message about humanity’s need to embrace diversity, by including Rahda, and also African-American actor Booker Bradshaw as Doctor M’benga.