I would argue the opposite: this is still wildly relevant today. People still look at people of color and women in their jobs as they did Mr. Tibbs - a range of disdain to low expectations. Very little has changed. I mean, he got arrested solely for reading while black, which still to this day happens constantly (and have triggered the Black Lives Matter movement).
What I like about the movie is what they said in the episode: it's not full of monologuing or preaching or whatnot. I found the police case to be realistic in that regard too -- instead of showing a racially charged murder to condemn racism, the movie focuses on a regular murder and shows the racism all around that. It's in the autopsy, in the coworkers and boss, in the victim's wife, in the interrogation suspects. If Tibbs showed up down there and solved a KKK murder case or something, that starts to push into melodrama. Instead, it reflects reality, showing us how deeply racism is embedded in the everyday routine.
That's also why I believe it gets a balance in not just being about racism. It is about a murder case. The comments on society just come along with that.