The problem with a rotation that is so heavy on TM, for me, is that there is a cast time on the ability. Casting what is otherwise a ranged attack when someone is in your face is just a silly dynamic. Yes, we have a couple of knockbacks, but a strong or especially a elite melee mob is still going to spend a lot of the fight within melee range of you (assuming you don't use a tank comp). The whole thing is awkward and, ultimately, boring.
I think merc would be more fun if TM was changed to an instant cast, on a short cooldown, forcing us to splice in rapid shots, allowing us to be more mobile, and perhaps giving us one additional kiting skill (a non-damage dealing slow on a CD) to encourage us to keep stronger melee mobs from hitting us to begin with. Nerf TM damage as appropriate.