train overseas or train locally.
The real question is "what do you want to do?"
If you are devoting yourself to learning Korean food, then Korea is where you should go.
If you are devoting yourself to being a better cook, then pick a high end restaurant in Sydney or another city with four star cuisine, high level cuisine and work there. As you will find on various threads here, working in a kitchen means the same thing everywhere. Good habits for punctuality, cleanliness, food preparation, pleasant attitude all need to be developed no matter where you are. Travel is great but there are good and bad restaurants everywhere.