I used to do the xbow shot right before am2 hitting. Occasionally, all the mobs would ignore me even though I hit first, and all go for the blackmage. I found it to be much more reliable for myself to xbow shoot x, kite half a lap, then start on the mithras (infact, we kill the wyvern first now, since it can heal all the mithras, and is a general pain in the nutsack)
As for blackmages - if you aren't a career blackmage with a full enfeeble build and merits, your bind is going to suck and get resisted often.
