Lounge staff would have no idea of flight planning issues.
Load restrictions would vary, but if they made a habit of planning full, then they’re going be caught out any time the weather in Sydney isn’t perfect. The only time I flew it, we were very comfortable for fuel, with a very full load. But, about 10% were staff passengers, who were not approved until I’d had a look at the paperwork.
The crew would have to get off it the flight departed with any plan to divert to Brisbane...extensions are only available on an unplanned basis.
Flight planning is not an exact science, contrary to what the fuel fairies would have you believe. It’s not at all uncommon to have a couple of tonnes of fuel just disappear. Held lower than planned, a wind slightly stronger, or from a different direction, or even a coughulative couple of tonnes of excess cabin luggage, will all have an effect.