Before you speculate about training, V1 cuts, asymmetric handling and whatever other nonsense think about the above.
Have a look at the
ABC story linked on the previous page, which includes the following excerpts:
The airline has confirmed [the crew] …were performing an "engine cut out on take-off" manoeuvre when their plane crashed...
The bureau's investigator in charge, Alex Hood...says the sharp left roll of the plane that caused it to crash is characteristic of an engine-out manoeuvre.
However he says a mechanical or systems failure could also be the cause.
Interesting how several posters were given a hard time earlier in this thread for suggesting similar thoughts to what the ATSB investigator in charge has stated above.