Why Australia would buy County-class cruisers

Would Australia build its own Hawkins-style or unique heavy cruiser instead of buying County-class ships?

No: without the necessary cruiser-building infrastructure, Australia would adopt the British design already supported by yards, weapons production, and skilled labor.

Australia had useful and growing maritime infrastructure, but not the complete industrial base to design and build a unique heavy cruiser at this date. Even Town-class construction strained the available yards, while a County-scale program also required turbines, armor, heavy guns, turrets, and skilled workers. A unique triple 8-inch turret would add another expensive development chain that Britain itself was not using. If Britain produced County-class ships under treaty limits, Australia would procure that supported design; without the treaty, it would more likely follow Britain's larger 9.2-inch cruiser program. Proposals for a domestic cruiser depended on a major prior investment in Cockatoo Island and remained political ideas rather than a ready construction option.