What was the justification for the large number of U.S. Marines casualties sustained in the effort to clear all the tiny Pacific islands of Japanese soldiers? Why not just take key islands over and cut off supplies to the insignificant islands with the dominant marine and air superiority?
That is exactly what happened and what the plan was.
Island hopping was based upon capturing select atolls and islands to serve as fleet bases and airfields until bombers could hit the home islands and the naval blockade and possible invasion could be easily staged.
Islands such as Guam, Saipan, Iwo Jima, and Okinawa were seized for exactly that reason, to serve as fleet bases and airfields for further advances or for strategic bombing. Major Japanese positions of strength were avoided when possible, and pacified by bombardment by ship and air, and cut off from supply or support.
In particular the great Japanese base at Rabaul on New Britain was a fine natural harbor with surrounding air fields and had been the HQ for the Japanese efforts to first hold Guadalcanal and then the entire Solomons/New Guinea region. It was never invaded and simply cut off and rendered impotent.
Another great example is the MASSIVE Truk lagoon, essentially the Japanese Pearl Harbor and advance base for the IJN, but despite its possessing one of the finest natural harbors in the world it was not taken, the defenses being seen as not worth it, and the war able to move past it with the US using alternative bases.
Additionally smaller positions such as the Japanese held Wake Island were also avoided.
Ian W. Toll's Conquering Tide is a good look at the idea and goals of Island Hopping.