It's amazing how different people's experiences can be. I've had countless flights with Qantas and nothing like the issues you mentioned, although all of my flights that I had booked and then cancelled in 2020 (the covid scenario) were not with Qantas and there were a few back and forth communications with the carriers to get my money back. Virgin Australia were a little difficult to deal with but I just assumed they were under additional duress due to the situation that spanned the globe.

I have to stand by my previous statement about Qantas, I've just not had the issues you have and on the occasions things have gone wrong they've been really good about it. I was once grounded in Sydney as there was a storm...they threw money at me for accommodation and food. Another time I'd booked a flight home (also ex-Sydney) at 07:30 mistakenly thinking it was 19:30. I arrived to check in and they were like, you're twelve hours late. No worries though, I paid for a new (economy) ticket at 35% off and they put me in Business Class. There's been other things, but they've generally been good. I can't complain.

Singapore airlines have been great though, as you say, one of the worlds best airlines for a good reason.