There's a solid reason why West Aussies are set on this classic, durable building material, but double-brick might not be the home of choice as the climate changes.
Short, but nice article on double brick housing in WA. It'll be interesting to see how the home construction industry here changes in the coming decades.
It’s mass that holds heat. Rammed earth is great if you don’t let it get too hot (so needs shading), or if it’s insulated (the best way).
For almost all of Australia bar the tropical north, the best construction is insulated mass - ie cladding (lightweight or not), then a cavity, then loads of insulation and a Vapor membrane, then masonry.
And my house currently has one of the four layers you suggest. I might just have to save your comment, i'd definitely missed the vapor layer and a cavity behind the cladding.