I've used TinyTip to show me how many people are targeting a mob. I believe it's in the Extras somewhere. You can show all the names (with color-coded classes), number of people targeting, or number of each class targeting. The downside is that you have to find the mob and hover the mouse over it to see the information you want. I did play just as a healer, not an MA, so I can't quite say if this will help in that position.