Say a successful candidate at QGPA who goes onto making a $106k a year job (using your figures) at the age of 25 (some are younger, some older, just an average), and retires at 65. Compare that to a "traditional" flight school where the student spends less money on training, but then finds themselves unemployed, potentially for a significant amount of time depending on luck/timing.
Let's assume they are successful in finding an entry level GA job, they will most likely make the single engine piston award (~$53k?) after having spent many months unemployed/pulling pints while paying out of pocket for living/moving expenses in remote Australia. That difference in earnings (~$50k) is compounded in favour of the QG student for the next 40 years.
Say by year 2, the GA student moves onto multi engine pistons/single engine turbines ($60k? $70k?) and the QG student moves onto year 2 FO ($110k? $120k?). That is additionally another $50k, compounded for the next 39 years.
Repeat etc every year for typical career progression and I'm sure you'll find the QG cadet comes out significantly ahead.
The main pitfall I see of course with QGPA is not everyone makes it. Not everyone who applies makes it to testing. Not everyone who tests makes it to the interview. Not everyone who interviews makes it in. Not everyone who makes it in graduates. Not everyone who graduates gets a QG interview, and not everyone who gets a QG interview gets a job. But if you are successful in all that, it's the best career path right now in Australian aviation.