firstly NATO aren't fighting that war , merely supporting it but their ability to do that far exceeds russias ability so I would say logicvally russia are the one very unlikely to win
I do agree with you however that it would be inappropriate for Oz to join , if we were eleigible which I'm sure we aren't
but as to GDP for Oz ..... Defence budget papers show spending for 2023-24 will reach$52.558 billion– 2.04 per cent of GDP – up from $49.131 billion – 1.93 per cent of GDP – in 2022-23.