Conversely, I, Contract law, Reality, Qantas and their conditions of carriage disagree with you.
The OP did not book a seat. He booked a flight, which you may also like to know isn’t guaranteed either, as the conditions of carriage make perfectly clear. The airline is technically under NO obligation to actually provide the product you pay for, lay alone a particular seat which they also make clear they can take away from you under the guise of rather obtuse ‘operational reasons’.
The OP very much gamed the system. He would never ordinarily be entitled or able to get row 4 but knew that at T-80 (which is ‘the’ system) he would be able to, even if T-80 was at some ghastly hour and he waited up all night to get it.
Seats are NEVER guaranteed. EVER. And to be frank, as the OP is a bronze member, neither should they be, especially in what is considered a premium seating area.
The false sense of entitlement here is as ridiculous as the OP thinking that he’s somehow special or got special treatment for being seated/allocated/scamming his way in to row 4.
Had he been more ‘realistic’ and chosen something between rows 6-10, it may have stuck, but I am neither concerned nor surprised he was moved from ‘emerald city’.