It certainly sounds like you have had a rough time with your renovation. Who was supervising the works and what was there level of experience in the building industry.
Unfortunately many people just go with the cheapest quotes hoping to save some money (a bit like buying things from China) but end up paying in the long run.
Without a doubt there are some rubbish tradies out there and unfortunately because of the current trade shortage many fly by night people will have a crack, being attracted by the "easy money".
Unfortunately it's pretty typical if boom times. In quiet times it's only the best tradies who keep getting work, in boom times people get desperate to find someone to just do the job.
Yours is a good warning that anyone building now really needs to check on tradies references, ask around your friends for recommendations and unfortunately be prepared to wait for good tradespeople. I know I'm booked for at least 2-3 months. Plenty of people are prepared to wait but if you are in a hurry people grab anyone who can do the job.
Your building experiences in the last year are not a fair judgement of the entire Australian building industry.