Altogether, assassins have 4 defensive cooldowns: Deflection (weapon damage), Force Shroud (tech damage), Overload Saber (lockout-free medpack), and Force Cloak. I use Overload Saber fairly aggressively, and I'm always surprised at assassin/shadow tanks who don't. Force Cloak is another uncommon one, but primarily due to the fact that it debuffs healing. It has to be used very carefully with full knowledge of what you're about to do to your party. I use it absolutely every time I tank NiM Kephess (twice in the same fight if my co-tank dies in the last phase). Similarly, I use it every time on NiM Toth and Zorn (to reset the medpack lockout), fairly frequently on HM Dread Guard, and every time on HM Writhing Horror (to avoid pulling off my co-tank at the start). Also, there's all the situational uses when you need to get someone up and the battle rez is down.
No question though, the bread and butter is Deflection and Force Shroud. Use and abuse the heck out of those cooldowns. A huge part of what separates good assassin tanks from great ones is an active knowledge of the specific fight and the timing of relevant damage (e.g. Force Shroud right before Savage Wounding is applied on NiM Kephess).
I have to disagree with you on the Force Cloak, in no way does it qualify as a defensive CD. You can count it as an advantage/exploit to get a medpack CD back or to circumvent the BR limit by doing an out of combat rez all you want, but it does not provide you with a buff to help you immediately relieve incoming pressure without compromising the raid itself. Listing Force Cloak as something good to use is exactly the line of thought that got Assassin tanks a bad name in my old guild and throughout my old server because some ******s thought it would be a good idea to actively use it (some serious and some because they thought it was funny)....
The rest though I agree with, the three CDs of the Assassin are Force Shroud, Deflection and OS with the main short CD is Dark Ward, and expert use of FS and Deflection makes for incredible results compared to the other tank classes in the same situation.