I agree in the principle, but that is not enough. You may trade 10 pairs then at some time you have positions on four one.
Unfortunately, the four pairs are about Yen. Then trouble arrive.
I dont trust at all diversification for extreme events. In fact it is like gaussian curve : it does'nt work exactly when you need it.
Diversification gives protection only if it is a massive porfolio : multi asset, multi strategy.