Back when 774 was a late night departure you’d get kicked out of the QF F lounge when the last Qantas plane left and had to go over to slum it in mahabra lounge. Now it’s early morning it’s less of a problem, but air New Zealand probably offer a better deal on lounge access than QF so JL send people there. Haven’t been in there for a while but IIRC the air New Zealand lounge is a bit nicer than the QF business one, it has a window at least.
Diamonds and OWEs certainly know where to go in any case. Whenever I take 774 there never seem to be that many top tier members. Pre Covid business used to be full of holidaymakers on the AY codeshare.