As a MNK, I'll happily punch whatever the tank marks up. I'll assume they have a reason, perhaps something unique to them, and makes little difference to me.

If I choose, I'll pick the mob that has the most annoying AOE first. So the massive monoliths with their big circle AOE go before the spriggen and its cone AOE, which goes before everything else.

As a positonal DD those scrums of mass pulls suck. Impossible to see anything.