Hm. My Tank spec Shadow uses Shadow Strike a ton in PvP and quite often as an opener in PvE.
If you've got Infiltration Tactics and the buff is up, Shadow Strike is a good attack. If you don't have the talent and the buff isn't up, it's pretty much worthless: it deals marginally more damage than double strike (though it doesn't proc PA so it's actually worse damage in the end run) and costs *way* more Force than anything else you use. In PvP, Shadow Strike can be somewhat useful since you can actually get to use it on a target beyond the opening strike. In PvE, it's worthless since you're not going to have the Infiltration Tactics buff while starting a fight (so it does terrible damage *and* gibs your resource maintenance) and enemies should be staring at you rather than showing you their backs for everything after the opening attack. You're actually better served just using DS, Project, or Slow Time as an opener in PvE (I generally open with Project on a single target or Slow Time on a group since it generates more than for less cost than Shadow Strike will while simultaneously generating an HS stack).
Force Breach is often used to stop groups of people trying to cap objectives, or to lay waste to hordes of weak enemies after a Slow Time. But, to each their own.
I never said that it would be *optimal* to use an Electrostaff rather than a DBLS. Force Breach *is* a useful attack, but it's not really all that big of a contributor as an actual attack since you've got Slow Time on a shorter CD that deals more damage. The biggest loss isn't from not having Force Breach: it's from not getting that 5% acc debuff.
Like I said, KC would be the *least* negatively impacted. It's still negatively impacted, but not to the same extent as either of the DPS specs.