I play a marauder and it is true that Mercs - however much I just hate tracer spam - have a harder time with kiting than other ranged class like Sorcs.
So perhaps they should give them a speed boost as well so they can use it like Socs do? - Stun - Runaway.
It would be a step in the proper direction but it wouldn't solve the problem that interrupting Grav Round/Tracer can effectly shut down your rotation because this AC is too dependant on said skills. Grav/Tracer either needs to have interrupt immunity or activation time reduction. I would go with a talent you can spec into that makes Grav/Tracer immune to interrupts and probably make Full Auto/Unload uninterrubtibe as well. The Knight/Warrior channeled skill, Master Strike, is already uninterruptible, so why not give the same to Full Auto/Unload.
The problem with dps is not so much the theoretical numbers this class can pull if left alone and played to its potential (altough it would never be as high asRage Jugg or Mara dps) but that this class is extremely susceptible to interrupts and if one happens, you're pretty much dead because you can't finish your rotation.
As for dealing with melee, Snipers are immune to Force Leap and Sorcs can Force Speed away, so Commandos would have to have some edge against melee classes. Maybe a 10 or 15 sec cooldown that gives you temporary jump immunity (something like Not One Step Backwards/Hold the Line) or just give them the already existing Rocket Boost with a shorter duration than in PvE, usable in combat of course.
The way I like to play my Commando dps is to stick to the side and back as much as possible and be as inconspicuous as possible (hide behind objects etc,). Then when an enemy group appears, start blasting them while they're fighting each other. It would be nice, however, if I could hold my own against a melee I'm targeting for a few more seconds, then run the hell away.