LeadSled
If the aerodrome traffic only justifies a D tower, by definition (low level) C cannot be justified over D, it is simply impossible for the approach and departure traffic, clear of the circuit area, the D zone, to present a greater collision risk than in the immediate D zone of the aerodrome.
Its not only about collision risk, it is about mitigating risk with the available infrastructure, resourcing and traffic levels. In that regard the US and Australia are about as similar as chalk and cheese.
Keep demonstrating your ignorance, it is certainly helping.