Hmm, without Shatner, there is no Star Trek.
Shatner was an acclaimed Broadway actor who had already made a name for himself on television before being offered the role in the second pilot.
Patrick Steward was an undistinguished character actor before TNG.
Avery Brooks was best known for a recurring role on Spencer for hire.
Kate Mulgrew was a last minute replacement for Voyager, was known for a stint on 'Cheers' as Sam Malone's love interest.
The latter actors all took off because of Trek, Shatner had a sucessful career before and after TOS.
As for who would win head to head, Kirk would in any contest against the later Capatins, all of whom could never match Kirk's natural leadership or excellent sense of tactics and timing (its all subjective, of course.)
As for being a 'womanizer' or jerk, 60s television required a certain amount of that, but they really made fun of this in the movies, especailly in ST IV and VI.
BTW, "Voyager" was a horrible show until 7 of 9 was introduced, and even after that, it was never top notch, it could be excellent at times, but it would snap back just as easily into pedantic.
I saw each show in order, so I can speak to it from that point of view, I can see how a modern gal might look down her nose at Kirk, but for the children of the 60s, Kirk, Spock and mcCoy will always be beaming down to some planet, and solving the unsolvable, beating the unbeatable, while performing in art-deco surroundings and on a ship that looks like a bad Ramada Inn on the inside.