Yes other airlines carry 2 CPT's and 2 FO's so that's very relevant.
EK and the USA carriers combined.
On a DFW-SYD you've usually been up for a lot of the day before you then do a 20 hour duty at night.
You don't necessarily get to take a break when you want to take a sleep.
Agree that your lucky to get 3-4 hours actual sleep when people are not banging around in the cabin and keeping you awake.
3-4 hours is not a nights sleep in a 20 hour duty.