Yeah, melee is good for the 'hit' - but anything slow enough for you to land that hit on will be tough enough to take the hit - Lights and most Mediums can outrun you, Heavies and Assaults can soak it at least once before anything vital is damaged. And then you're stuck with the 'Run', giving them a juicy opening to pour fire into you unopposed while you try to build distance for another hit.
For real Hit & Run tactics, the lighter the better, and as much range as possible. Speed lets you rush in, deliver a strike, then get out before the target ranges on you...repeat as necessary. Range lets you get better targeting solutions than your prey, so you'll maintain accuracy advantage to compensate for your weaker armor.