Taildragger, you have got it bass ackwards. Qantas can play with J* International, Australian etc., precisely because it has an effective monopoly on capacity. In an unregulated market, the idea of a "low cost" brand of the same airline would create market confusion.
ie: Is j* as safe as Qantas?.
Is J* International different because of the food/seat pitch/baggage conditions?
In other words, why does Qantas have a low cost brand? What is missing? Is it the expereince of the pilots? What have they "cut" to give a lower fare?
In other words, you get cognitive dissonance. Ie: What is the difference between flying with Qantas and fkying with Jetstar?