The longest it's ever taken me from aircraft to exiting arrivals is 15 minutes at SYD, and that was when half the SmartGates were removed for upgrading. I arrived last week in the busy time and from stepping off the plane to exiting arrivals was ~5 minutes.

The biggest delay is inbound holding and then ground holds waiting for a gate if something is late leaving. A bus bay would also ruin ones day.

I agree 3 hours is the safest INT>DOM transfer time at SYD.