To be totally fair, Unremitting/Unstoppable makes them especially helpless against Vigilance/Vengeance. Even more helpless than against other melee classes. And they have no defensive cooldown to negate the Master Strike/Ravage that surely follows immediately.
Due to the overabundance of Smashers, most Mercenaries now use knockback or stun immediately when they see a leaper - can't blame them but it's a death sentence against Vigilance.
I wouldn't do that against Venegance because the animation of Unstoppable is clearly visible but Vigilance is a bit more confusing because those aura animations of jedi sentinels looks pretty the same to me. I agree that we lack defensive cooldowns. The shield is simply not enough. Jet boost is useles on flat ground. Concussion missle is useless due to long cast time and interruptibility (really not worth spending the instant cooldown on this skill). Electro dart not too much of a use due to 10m nerf. Rocket puch is 4 secs which gives you enough time to get away, but that is about it.
All this just shows how unexperienced BW is with MMOS and especially PvP balancing melee vs. ranged. As an example I would set WoW and all the skills mages and hunters got there to keep melees at bay. Mercs cannot even compare to that with the lack of skills and many of useless skill you still have at lvl 50 which you don't even get to your skillbar.