Pike was obviously less of a womanizer (he was given his choice of three women, after all, and chose none of them. Compare to Kirk and his girlfriend-of-the-week.)
But look at
early Kirk -- he was just like Pike. In "Mudd's Women," he was the only man other than Spock who wasn't gaga over the title trio. He had his work to do and couldn't be bothered with the distraction of the fair sex. In "The Corbomite Maneuver," he complained about being assigned a female yeoman in the same way that Pike lamented about women on the bridge. In "The Enemy Within," it was his unleashed dark side that came after Janice in a way he never would have normally, and in "The Naked Time" it took an inhibition-releasing virus to get him to admit his yearning for a hand to hold. In "The Man Trap," when Salt-Vampire Nancy first appeared, Kirk saw her as a mature, ordinary woman and it was the younger crewman who saw her as a sexy siren. In "Charlie X," he was uncomfortable about being placed in the position of the father figure having to explain about women to Charlie.
It wasn't until "What Are Little Girls Made Of?" that we saw the beginnings of the familiar "Kirk makes out with spacebabe" meme, but his seduction of Andrea was a calculated tactic to exploit the androids' weaknesses. Then came "Dagger of the Mind," where he was embarrassed about having simply danced and flirted with Helen Noel at the past Christmas party; what a lot of people misremember is that the flashbacks of the two of them getting hot and heavy were a fantasy created by Helen, implanted in Kirk's mind by the neural neutralizer. The whole point of it is that it was something that never would've happened in real life, so that they could confirm the machine was capable of putting false ideas in people's heads. Then we had "Miri," where both Miri and Janice were trying to get Kirk's attention but he was too busy with the crisis to respond as they wanted. Then "The Conscience of the King," the second time Kirk was shown actually romancing a guest star, but again it was a ploy, a tactic to investigate Leighton's death and his charges against Anton Karidian.
Finally, in "Court-martial," we met an old flame of Kirk's, the first indication of any actual, successful romance in Kirk's life that didn't involve deliberate deception or mind manipulation -- and even that was many years in the past. Then after that, in "The Menagerie," we had a brief bit of a starbase crewwoman alluding to Kirk's reputation with women -- the first hint that Kirk was a womanizer, and it was halfway through the first season. Right after that came another old flame, Ruth in "Shore Leave," but she was portrayed more as someone he'd genuinely loved and longed for rather than a casual fling.
After which came a string of ten episodes in which Kirk had no romances of any kind (unless you count a slight flirtation with Mea 3 in "A Taste of Armageddon"), a streak that was only broken by "City on the Edge of Forever," in which he fell deeply and sincerely in love with Edith Keeler over the course of a weeks-long romance. Again, hardly the behavior of a girl-in-every-port womanizer.
The "different girl every week" Kirk of popular mythology didn't emerge until the second season, and even then, it was far from every week -- Sylvia in "Catspaw," maybe some Argelian girls offstage in "Wolf in the Fold," Marlena in "Mirror, Mirror," Drusilla in "Bread and Circuses," Nona in "A Private Little War," Shahna in "The Gamesters of Triskelion," Kalinda in "By Any Other Name" (though his seduction attempt didn't achieve his desired goal and she ended up preferring Rojan to him), technically Thalassa in "Return to Tomorrow" (though that was Sargon in Kirk's body), and that's about it, less than a third of the season. Season 3 wasn't too much different.
The thing to remember, of course, is that pretty much
every 1960s male adventure lead was expected to be a womanizer and a brawler. Look at Jim West on
The Wild Wild West or Napoleon Solo on
The Man from UNCLE and you'll see a lot more womanizing than Kirk ever engaged in -- certainly far more than first-season Kirk. Kirk started out being the same character as Pike, but over time, mainly in the second and third seasons, he came to be written more and more as a conventional '60s action lead, because that was what network and advertiser pressure and the habits of freelance scriptwriters probably influenced him to become.
So if Hunter had stayed in the role, it seems likely to me that his character would've developed in the exact same direction. Hunter's personality wouldn't have lent itself to that change as easily as Shatner's did, but it was pretty much inevitable for a '60s action lead.
