I don't know that either is a breach of contract in the sense that in the first instance, which I call a "commercial requirement" the passenger is not inconvenienced in terms of the purchase of transport from point A to point B on a flight within a reasonable time of the schedule. The 2nd isn't a breach if the carrier can prove there were no other options available (eg: you were stuck at LDH because weather forced the inbound to cancel). I also don't know that ethics come into either of these examples, unless you want to argue the case that a a/c sub due to, for example, capacity planning causes someone to be downgraded from a 330 suite product to 737 J I think no there's not an ethical issue there. Now if an equip sub forces a confirmed upgrade to be lost due to lack of seats on the new aircraft, then absolutely compensation is due but I don't see this as an ethical issue.
With this specific situation in mind - let's say the OP had gotten a call at 7pm the night before and told we need to move you to the 0700. I think the customer has the right to say "No, this does not suit us, what is your next option?" and QF would have to come to the party (they probably would have offered the next day's flight, which in hindsight would have been bad given it didn't run). I know the original flight wound up running, but there *must* have been a reasonable reason that this was no longer an option. This is where we just don't know and it's not fair to anyone to draw conclusions or make assumptions I think. On the surface this is a major screw up, and at the very least an involuntary change like this demands for compensation - notification aside this was not the customer's choice.
So QF need to come to the party on that alone, let alone the questions over notifications of the change which become even more murky given the multiple TA's involved. I think QF could suggest they put a SSR into the booking that was agent controlled to notify them, and basically "we told the agent via our usual process and it was their responsibility" - I'm not saying this is fair, but I can see how QF could consider that a notification of change being made. Since they did not"own" the booking, it may well be that their protocol leaves it to the issuing agent.
Seems like a perfect storm here of a (apparently) poor decision made on that Sunday night then somehow this was not communicated to the customer and it seems like it may have been a case of "the other guy would have done that" in play rather than "we'll just call to confirm"
question marks aplenty.