My concern is that I truly and deeply believe that when these people were so intimately involved (100 hrs per week or more sometimes) on a series and/or movie, the strength of the relationship would last for years or even decades. But as read on this and other Threads, the overwhelming majority of you do think this should be the case.
But Takei
wasn't that involved. Shatner made the point at least once, I forget where, that years - now decades - of fandom and cheering conventions and Takei's public image have elevated Sulu to a position he just didn't have at the time.
Now, Takei/Sulu's 1/7th of a classic team of immortals, but
then, he was just the helmsman, who got a line here or there per episode, and a few moments out of three seasons to shine, but that's it. At the time, long before anyone realized how long-lasting
Trek would be, Shatner thought of it as his show with himself and Nimoy and Kelley as the stars because
that's how it was.
It's also probably not a coincidence that Shatner had by far the most dramatic and longest scenes with Nimoy, and has been better friends (maybe
only friends) with him ever since. Not that working so much together fated them to become besties, of course, but I'm sure it played a part.
As for the rest, it's all context and individual personalities. But
TNG set template for
Trek shows as ensemble series, whereas
TOS had been a
trio show with recurring background cast.