Sage/sorc shouldnt have any problems with killing others. I play shadow and when i start to hit sorc, first that stun bubble stuns me and sorc hits a lot. then i start to chase him/her but he/she uses force speed and has a couple of seconds to hit me. After that i go after him/her again but he/she uses knockback and cant move for 5 sec and when im able to move again, he/she hits me again. And IF im still alive after that, another stun bubble stuns me and sorc can hit me again. And ofc sorcerers have normal 4sec stun and that 8sec one if my resolve isnt 100% already...
Im not saying that i never win sorc BUT im telling that its not hard to a sorc to kill others.
Learn to play issue.
As a shadow you should not have a problem facing sorcerers. You need to be smart about your burst. If your running deception do not open with voltaic slash. It is incredibly easy to tell who is a bad Assassin player by how they open on a Sorcerer or any bubbled opponite for that matter. Assuming this is your first engagement assume they have a stun bubble.
What does this mean?, it means you pop the bubble using shock or some other skill from 10 meters. You save force shroud for the rebubble, slow and knockback root.
If you are a Darkness or Darkness hybrid and are having problems with Sorcerers/Sages, you'd better just stop playing your class and play sniper. Your ability to pull a kiting sorcerer to you is an instant win. If you cant figure out how to use it properly or find yourself loosing even when you have it, you are very bad at playing your class.