The better ones will be employed.
Those who undertake the ATOs aptitude testing really need to pay attention to the outcome. If you are assessed as a training risk, that translates, in percentage terms, into not expected to exactly flourish. You really need reasonable expectation of success, and the potential to be employed.
Do the sums of cost of training, against reward. After all, it is not exactly cheap.
End of the day, SUPPLY and DEMAND will determine whether the marginal ones get employed.
You will always get the "no hopers" who struggle throughout the course, but decide to take the risk: as ever, it is a personal choice as to how you spend your money.