OK, that range bit is strange.
The F-35A has a longer unrefueled range than the F/A-18E/F - and the RAAF has just bought new air tankers that can refuel with both boom and hose, so "extended range missions" are just as possible with either type.
And since the F/A-18E/F is going out of production in a couple of years, how would it be easier to replace those than it would the F-35 - which will be in production past 2030?
And just FYI - the RAAF has no F/A-18Es (single seat) - they have F/A-18Fs (two-seat), and are getting EA-18Gs (two-seat EW versions).