Interupt his ****, noobs.
Tracer Missile is fine, learn to play.
I kill mercs all the time (on a Guardian at that, so any other class can do it), 1-2 interupt is all you really need, knockbacks, knockdowns, force push, force leap, anything that moves them around or interups their cast = easy kill
Remember that they have to stay stationary in order to use it, meaning you can use all your big nukes on them and they won't even move around 90% of the time.
This whole Tracer Missile issue is just a big Learn to Play sign.
I'd be tempted to say the same about sorcs if they didn't have force speed and their bubbles.
Flame on.