Yeah, the argument is that for some reason HMAS Australia (I) - the battlecruiser - would be a better premium. I don't think so personally, she was just representative of a fairly numerous line of battlecruisers - including HMS New Zealand!
HMAS Australia (II) at least had something of a war record to point at as a premium.
Personally, even as an Aussie, I'd vote HMS London (rebuilt) as the Heavy Cruiser premium.
So could you have premium wise for Commonwealth cruisers/battlecruisers:
II- HMAS Sydney
III- New Zealand
V- Achilles in 1945 configuration (would be an AA ship with DFAA, Achilles's X turret was destroyed and was replaced by AA)
VI- Perth or maybe Sydney II
VII- Canberra or Australia
VIII- Perhaps a London refit with significant buffs could work here?