Plus, shouldn't Sulu, Chekov, Scott & Uhura be included in the secondary cast list? As has been mentioned earlier, they were all hired as day players, not main cast.
To be pedantic (hey, this is the internet!), that's not quite right. William Shatner and Leonard Nimoy were the only regulars during the first season (DeForest Kelley would be elevated to being a regular in the third season), but they weren't the only contract players.
Whitney and Takei were both hired with series contracts, as was Kelly, and James Doohan was hired with a multiple episode contract. Only Nichols was a day player throughout the series. Koenig was a day player during the second season, but he was given a contract during the third season.
Still, this didn't make them regulars, and despite statements to the contrary, Star Trek
was never an ensemble show.