About 5% of people that apply pass CTC selection, of which 98% pass the entire course of which 100% have been placed by an airline (who are not currently in the hold pool).
Not much advantage of having a PPL except for being able to show that you like flying. Only a minority of students per course have significant flying hours behind them. One thing to note is if you have a PPL some of the foundation course could be refunded to you depending on your ability which would be assessed during your initial flights in New Zealand.