All I can suggest about your dilemma is that if there are no QF Group jobs on graduation from the Qantas course (very likely to be the case), then you will be looking for a GA job just like you would be on graduation from the other course.
However, when the time comes that QF Group start hiring, someone in HR will fish around in their bottom drawer and find a list of names, and you will be a known quantity to them, so (assuming your reputation is good) you will probably be hired sooner than otherwise.
Will having the QF course in your logbook be a detriment to your employment prospects with other operators? Who knows. Probably not a detriment to a GA job, but could be a detriment to a later turboprop job if the employer wants to keep you and is worried about QF phoning you 6 weeks/months after employment.
Pros and cons, and no one can predict the future in aviation. If I had the choice and airline flying was my goal, I’d choose the QF course, but you may get different opinions from others.
3-6 month wait isn’t going to make much difference to your career because we are in a slump. If we were at the beginning of a wave then that 3-6 months can make a big difference.