I can't comment on QF J in LAX as I've only ever used QF F there but it would have to be pretty bad to justify walking over to the Flagship lounge which, last few times I've been there, was nothing special at all in any department.

Actually, I take that back, it has a passable view of the tarmac. But the food and drink was very disappointing in my eyes (though, comparing with a sit down meal in QF F in LAX so point of comparison is perhaps unfair).