When I play Japan, I find that ANZAC is really hard to deal with. Especially once USA is in the war. You get so busy dealing with the US Navy, trying to stomp out China, go after India and get and keep the DEI, that you don’t really have time or resources to deal with ANZAC. Yet here they come in little bits. A sub sinks an enescorted transport, trapping valuable troops on some island. A transport with a couple of men takes Java or Celebes, wrecking your DEI NO and taking valuable IPCs from your income. So you have to try and escort every transport, send destroyers out looking for subs and leave garrisons on your DEI conquests. Those men might be better used elswhere.
Plus, if you go down with a significant force to try and spank ANZAC, here comes the US with huge fleets possibly threatening Japan. Whenever I have tried to take out ANZAC, it usually gets me into trouble because I have to commit too many resources for too little gain and leave other, more valuable areas weakly defended.