Gazumped
You seem to think that one has to have or declare a fuel emergency before doing what QF did.
That's simple minded logic.
The rules state that only in an emergency can one descend below MDA. An emergency could be any number of things.
You can argue that QF had an emergency as they did not have diversion fuel and the weather was getting worse.
So they made a call in the interest of safety.
Pure and simple. Good call in my opinion.
As I said you can apply your logic and land with 535kg or apply the QF pilots logic and land with 2 tonne.