As a level 40 claw/regen stalker I have more problems handling the 10+ longbow that charge in at the same time, taking down the hero seems easy in comparrison using focus/shockwave to keep him knocked down while killing any other mobs and then just placate/AS then scrap it out.
Another option is once you zone into the mission, head straight into the police staion and down the lift, kill the boss/lieut/minion that are there and then break out the boss (silent blade i think) you now have a very nice tough pet. Altough the pet does stop randomly to attack any objects on the map, it makes a great distraction when fighting all the bosses in the mission.
Neddy