AIP,
If you choose ( as I do) to use air safety outcomes/accident rates (using ICAO criteria --- not the "tailored" definitions occasionally used elsewhere) whatever US is doing (FAA + US AOPA + NBAA + NTSB + all the other contributors to air safety), US IS world's best practice.
If you doubt this, all the statistics are available from the most significant of the relevant published material, that most advanced aviation nations make available. Without any preconceived outcome in mind, go have an unbiased look, you might be very surprised. Make certain you compare like with like.
There is only one area where we beat the US, and that is gliding
Within US, huge volumes of movements are accommodated, the MAC rate is so much less than Australia, that the difference cannot be written of as "sampling error", by whatever name. The rates quoted by the CASA DAS/CEO will surprise many, he is correct. Why wouldn't he be correct, he is only quoting publicly available data.
Being largely concerned with international transport, much of the ICAO docs. have little to do with GA. Indeed, the Chicago Convention of 1944, at the height of WWII, did not have GA as a high priority, at least in part because GA as we know it didn't even exist in 1944.
There is absolutely nothing to suggest that ICAO D is in any way optimum for a GA (or any) aerodrome, nor is there anything improper in filing differences to meet national objectives.
GAAP is FAA D, with minor variations, the movement rate caps are not intended to be permanent, once mitigations for the problems detailed in the Ambidjii report are put in place, I am certain there will be changes to the movement caps.
I feel very sorry for those who are disadvantaged by the caps, let's hope everybody smartly gets together to get the mitigation in place. A few CFIs understanding the GAAP "rules" would be a start --- see the Ambidjii report.
Tootle pip!!