BA/QF do not dominate UK-AUS. SQ, CX, MH, TG and others are very large participants in the market. SQ derives 25% of its revenue from the "Kangaroo Route".
BA/Swiss would also be markedly different to BA/AY - Finnair is not really a choice to go US-Western Europe with. Swiss would definitely be though. Therefore one could conclude BA should be okay with AY but less so about Swiss.
I'm not suprised. BA is by far the senior oneworld airline in Europe (greater than AY, IB and EI together IMHO). It has far less bargaining power with Swiss involved.