There are plenty of those fotm sents/maras out there to hunt...and gs/sniper has plenty of roots, slows and stuns to deal with them.
I prefer to hunt out the other dps'rs that can destroy me...kinda offense is the best defense. I would much rather get in some big hits on those sents/maras and force them to use their defensive cool downs so I can root/stun them. Much better to be the first punch in a fight imho.....if you wait for one of those classes to get on top of you before you switch to them...you are already dead.
That hybrid build I posted...is a pretty nasty opening rotation that can kill all but the beastliest pvp'rs out there if you can hit them with ...shock charge, vital, shrap, sab charge, wounding shots...that will typically take them to <30% hp and you can then hit them with your Quickdraw/Takedown?(not sure what the finisher is called for sniper)....then switch targets because your bleeds will finish off whatever hp they have left.
Sounds like a long rotation, but all but wounding shots is instant cast so it really happens in a few seconds.
Using a modified version of your build, (Cooldown on stun instead of flashbang thing, Got endurance over cover pulse) how does it handle healers?