alot of it has to do with practice and of course proper gear. For example i also have a sentinel that ive been playing smash spec on since beta. I never played watchmen and when i try to play it i dont do very good. On my shadow, as of lately ive only been playing balance and im starting to get alot better. As far as gear goes ill post a screenshot later if you would like, but i have 1114 expertise, 150 crit, 1050 power, and 1900 willpower. I use alot of pve armorings because i find myself haveing better results with around the 1100 mark.
EDIT: Heres a screenshot of my current gear. I dont have any elite war hero gear, and the only datacron i have is the plus 10 on the fleet. This was an alt up until recently so his gear isnt amazing. But this is what it looks like ^^
http://i.imgur.com/Pun3R.jpg