What MacArthur and the Australians need for a campaign against Darwin is not what the Central pacific campaign needs. There will be little if any need for amphibious lift for MacArthur until Darwin is taken. The Central Pacific campaign has little use for land based fighters and USAAF medium bomber, trucks, railroad equipment, etc which is what the Darwin campaign needs. Of course there some overlap in things like munitions and fuel, but I do not see how the overlap material going to Australia is going to slow the Central Pacific campaign overmuch.
No disagreement here. Central Pacific route goes as planned, maybe even a little faster if the campaigns in the northern Solomons are butterflied away because once the southern Solomons and Port Moresby are secure and the Japanese are cutoff from getting to Australia from that direction, there is not need to go further. MacArthur's campaign is attached to the liberation of Darwin and he goes for the liberation of the Philippines from the south instead across the top of New Guinea.