Been back in the US flying for United for 2 years after almost 6 years at Virgin in Syd, so a couple of personal thoughts...
Mesa is a $hithole of a company. I very much doubt you could find a job in the developed world where you'd be treated worse, by your employer.
Don't make the mistake of comparing AU$ to US$. I get paid slightly more here as a 3rd year 75/76 FO than I did at the top 73 level at VA but pay 60% less taxes and support family of 3 on one salary, very comfortably. Your pay goes far further here than it ever would in Oz. Do find myself missing the lifestyle of a DINK in Sydney though.
Southwest coming to Oz???!! Not in a million years. They have a room full of CV's from guys here, that would literally sell a testicle to work for them. That's probably just wishful thinking from some less informed VA guys that still think Southwest is the best company in the world.
I will say this, though. I've spent almost 20 years here. On and off and I've found that since a certain numpty took office in the Whitehouse, I've had far more xenophobic and bigoted comments thrown my way about being a foreigner in the US. It's all the more surprising as I've always taken the approach of being extremely respectful, keeping my head down and being as anonymous as possible.