In addition to the drain on the UK economy facing Germany, there is another factor as well…
In order for the Australian IC to not be quickly lost, the US is going to have to spend a pretty significant amount of IPC’s on naval, AF, and even land forces to be sent to the South Pacific to help protect that IC.
Pulling half of UK’s resources off of Germany, and probably half or more of the US forces off Germany means that Russia is in deep Kimchee.
And Germany being able to nearly ignore UK and US for even a couple of rounds will MORE than make up for the minor easing of pressure on Russia’s eastern borders while Japan diverts forces to Australia.
Russia cannot stand alone against Germany.