I do not necessarily think Qantas owes anyone an explanation as to why the passengers were moved other than the standard 'operational requirements' disclaimer.
I would expect them to take responsibility and compensate for the initially missed flight, however, and then provide whatever cooperation is needed to assist with a travel insurance claim. Reasonable notice was not given.
Agree totally with the 2nd part.
Agree partially with the first. Operational Requirements make little sense if the originally booked flight went out as scheduled.
To me, the coverall of operational requirements can cover things like delays (not the case here), aircraft subs (unlikely, as I think only a certain size a/c can do this flight - a DH8?), seat swaps(goes without saying) and similar.
I think the real beef here from the OP is not so much the swap to an earlier flight (afterall they would have got there earlier) but the lack of confirmed notification. One can argue that in the case of a flight delay, or even rebooking to a later service, that even if the pax don't get the message they show up for their flight and the worst case is they wait - still a real hassle and annoying, but they get their flight. This is different when you expect and plan to get there for an 1140 departure but you've been moved nearly 5 hours earlier - that's something else totally - specially with barely 12 hours notice... but even then if they'd gotten a nofircation they could at least deal with res and say yes this works, no it doesn't, or whatever.
I'd want to bloody well know why I was moved to an *EARLIER* flight. Sure they can cover it with anything, but I'd be annoyed if I got the "operational requirements" bS specially when one sees the original flight went out as scheduled (but I do wonder about an equipment swap of some sort now maybe to one with less capacity?)
Plus I've found when it comes to customer service that more often than not must customers when given a reasonable explanation for something going on are reasonable about it - specially if it makes sense and is timely. It's when you're told nothing or given the run around it really makes things that much worse.
For example, if I was on that flight and I had a call say 8pm the night before saying "We're terribly sorry but we need to move you to a 7am service tomorrow because due to today's flight being cancelled, we're running this service at 7am, but we've had to use a smaller aircraft for the flight you were booked on and there's now not enough room on it, is 7am OK for you?" I think it would be a PITA, but at least would make sense (and of course you know there's a change!)
Maybe QF don't have to go into full detail, but gee I'd want a reasonable explanation for a change like this (quite apart from the whole lack of notification issue)
and just on that, let's say QF generated an email to the OP (though with 12h to go they'd probably also send a text and you'd hope for a phone call tbh) - email is not always 100% reliable. What if the OP's ISP was down for a few hours, or the email went into a spam mailbox, or the OP simply did not check their email - not everyone is connected 24/7 etc - one can not assume. I'd want to know what form the alleged "notification" took - is there documented there? Got to wonder.
my 18c worth