In reality gentleman's agreements are a load of BS anyway. As if QF will delay courses or park aeroplanes so they don't recruit some arbitrary number of Eastern pilots.
If QF (or any airline for that matter) REALLY wanted to hire you they will, end of story.
Additional to that has anyone actually tested this theory? ie Worked for a QF regional never got called, then changed employers and QF magically calls them a week later? Or is it just people who would never get in anyway somehow justifying why they can't get into QF Mainline?