Maybe Jetstar had only dearer seats available because the cheaper ones were so popular that they sold out !
You can rant and rave about Jetstar , or any other LCC for that matter, as much as you like but the only determinant will be the flying public. If they are happy to buy the cheap seats, they will. When the cheap seats are gone and the price of the seats left is similar to QF's, they again have another choice to make. If they all rush to QF, then the LCC will have to change it's pricing/seating structure to counter that ... and so on and so forth ...
Let the market, including you, decide!
P.S. Have you ever thought that there may be other reasons (than price) that customers choose a LCC over QF?