Keg, that's a load of you know what that because these cadets are senior they get allocated to the 'senior aircraft'!!!!!!!
Qantas place you on the aircraft they chose for you. How they choose that aircraft type for you, well now that's another issue.
In fact they have a history of starting some people a day earlier than others to give them a couple of seniorty numbers up and then putting them on the lower paying aircraft (ie classic and 767) whilst the others go to the 744. The ones going to these other types (classic/767) tend to actually be the more experienced pilots compared as a whole to the ones who go to the 744.
So as for starting a large group on the same day and seniority then dictates who gets what aircraft...hhhmmmm