That would depend on loads. If LAX-SYD is full then they can hardly carry you on that flight.
LAX-AKL flight might be held back for JFK connecting passengers depending on the length of delay and how many connecting passengers there are, especially since it is now being promoted as a convenient connection.

Edited to add - I think AKL flights have reverted to using TBIT now? (Presumably just to make the transfers easier.)