I beg to differ. I think they were similar, but not exactly the same. Kirk was more serious in the beginning, but he also had a sense of humor and at least cracked a smile from time to time.
First off, a lot of that was a difference in the actors' interpretations. Pike has a few lines that could've come off more whimsically had Shatner delivered them, like "Now you're talking like a doctor, bartender."
Second, as Nerys Myk
says, we can't assume the way Pike was portrayed in "The Cage" was his normal personality. His crew was recovering from a violent incident that had taken several lives, including that of the captain's yeoman. He was in mourning, he was bitter, and he was wondering whether it was all worth it. But as we saw at the end of the episode, his "vacation" on Talos IV shattered his illusions about another life being better than what he already had, and he returned far more content than he'd been at the start.
Hober Mallow wrote:
While I think that makes Pike more realistic, more human, for the kind of adventure show NBC and Roddenberry wanted, I think in the end they needed Kirk to be the captain, someone who isn't going to question his own command abilities.
Are you kidding? Kirk questioned himself all the time. In "The Naked Time" his big freakout was about resenting the burdens of command and just wanting a woman to hold and a beach to walk on -- that sounds exactly like how Pike felt in "The Cage." In "Balance of Terror" he expressed plenty of doubts about his command judgment and needed McCoy to talk some sense into him, just as Pike needed Boyce.
And realistic and human was exactly
what Roddenberry wanted. His goal from the start was to make an SF show that was on the same level as the most acclaimed, serious, naturalistic dramas of the era, as far as possible from the cartoony, fanciful stuff like Lost in Space
. He used comparisons to the acclaimed drama Wagon Train
to pitch it and the series bible encouraged writers to approach it with the same character realism and credibility they'd bring to writing for Gunsmoke
or the documentary-style police drama Naked City
. The show strayed from that somewhat in the latter seasons, and the movies even more so, which has led to the modern perception of the TOS cast as larger-than-life space-opera heroes. But they were meant to be very naturalistic characters, believable people doing a job that just happened to be in space, and in the first season you can see that very clearly.