Fantasy Island was a Genre Show, and often had More plots going than just different ones for the Guest stars. IE: Often a Plot of Tattoo being given an important Fantasy to oversee being granted, or A Maid finding Love or Mr. Roarke showing a Dark or mysterious side, etc (Though, Dark Roarke was far more directly shown with the Malcolm McDowell Remake)
was dark in the original series as well, especially the pilot movies.
The Love Boat also had a Ship's Crew Plotline, along with the Guest plotlines, which often developed the Crew's Characters.
And those started a Decade + earlier
The less said about The Love Boat
, the better; I'm sorry I ever wasted my time seeing that show as a child. Having B-plots on it meant nothing as the show was written 'for a child of five years old by a child of five years old' as Gale Gordon
put it in an interview for the Toronto Star
back in the 1980's (he was asked if he ever wanted to be on that show, and what he thought of TV then.)