The thing about a bonus is that it can be taken away at the whim of management, unlike salary to a great extent. It is the same with overtime, as your hours are 100% controlled by the airline.
The advantage to the airline is that if times get tough, they can reduce overheads dramatically without cutting staff. This avoids the cost of redundancies & leaves staff in place for when the industry picks up again.
The disadvantage for the employee is that they are taking some of the financial risk in the event of a downturn in the industry or even bad management. So, in effect, you are betting some of your income on things totally outside your control.
You will need to be able to live on the base salary alone if you sign up with JetStar & plan on sleeping at night.