As we all know the credits listed Shatner, Nimoy, and later D Kelly, as the stars of the show. Do you think the remastered versions should have stuck Scotty--Uhura--Sulu--Chekov in the opening credits when they were in an episode???
It's a meaningless and invalid question. Credits aren't determined based on opinions or whims, but on contracts and money. The contracts that determined who got what credit in TOS were negotiated, signed, and executed over four decades ago. The credits that exist on TOS episodes are the only credits they can legally have. Maybe, hypothetically, the contracts could be renegotiated, but it would be prohibitively impractical, perhaps even impossible, because many of the original parties to the contracts (such as the Desilu corporation and Gene Roddenberry) no longer exist and the lawyers who negotiated them would all be dead or at best retired by now.
And even if it were possible to go through the extended legal hassle to negotiate a credit change, what would be the point? All the actors in question did get proper credit that was commensurate with their contracts and status in the episodes, and they were paid what they had earned. They weren't deprived of anything. One's position in the credits is relative to one's salary, not one's prestige. There's no way to go back in time and change what these actors got paid for their work, so there's no reason to give them artificially elevated credit status that would have no tangible effect anyway. They were credited fairly and appropriately.
Also, as you say, the supporting cast members weren't in every episode. They were recurring players, not regulars. What, are you proposing that they hack up and loop the theme music to make the opening credits longer in some episodes than in others, in order to fit more names in?
