Mr. & Mrs. Howell -- Wealth and leisure class
Professor -- Academia
Ginger -- Entertainment and media
Mary Ann -- The heartland of America
Skipper -- Government management
Gilligan -- Incompetent civil servants
His premise was that Mary Ann was the only one on the island that actually made things work, while everyone else did little that actually mattered, but thought they were important, except for Gilligan, who did his best but screwed up everything.
In the pilot, The skipper, Gilligan and the Howells were supposed to be the main characters. The professor, Ginger and Bunny were minor characters. Ginger and Bunny were secretaries, and Bunny was supposed to be a sex bomb bimbo with a good heart. The professor was supposed to be a hunk. Those three parts were recast after the pilot, and the professor, who was originally a high school teacher, was made a college professor, and the two other female parts were remade.
The appeal of Gilligan's island, I thought, was pretty simple. All the characters were likable. The two girls were pretty, but not slutty. The plots were simple and anyone could understand it. The actors were all excellent at playing very broad, shallow characters in a way that gave them personality and depth. With only three networks, a show only had to beat out two other shows to capture eyeballs.
Gilligan's Island was an odd little show that wasn't quite like anything else on television. The network didn't want to run it, but decided they had to because the pilot tracked well in testing. Even then, they continued to interfere. The network insisted on the guest stars, and tried to give Gilligan a pet dinosaur.
A pet dinosaur? LOL. Glad they didn't go with that idea...