Cadet schemes can and do work. The essential requirement is very close supervision/oversight/monitoring/mentoring from the sponsoring airline at all stages of the cadets training.
Unfortunately this kind of supervision costs money and considerable time, and as we have seen with Jetstar's endorsement training, Jetstar put in minimal to no effort before the pilot turns up to work for Jetstar with the endorsement in hand.
That it appears Jetstar management view the cadet scheme as another revenue source to then provide a pool of cheap labour, indicates the scheme will be full of problems with poor outcomes.