Also with your ratings there, are you only considering purple gear pve gear your get from raids or pvp gear?
Im only asking cuz never in any gear that I had since 50 (or even getting to 50) did i have 0 shield and very little absorb. In fact you will always, at least as a sin tank, have much less def than shield and absorb.
If we take my character for example, he has green and blue implants, earpiece, bracers, belt, and orange head, hands, chest, pants and lightsaber. The mods on the gear are from daily badges or daily heroic rewards. My rating were about (from the top of my head as I cant see the stats atm) def= 175 shield = 225 absorb = 219. So my total rating is 619 yet your 600 rating is 400 def. Where on earth can I stack more def to get to raids where all my mod slots have at least +21 def. Better yet you don't take shield into account here and thats my best rating.
I also thought that as a sin tank you should focus more on shield and absorb since you have dark ward and since it takes a massive amount of def to get you close to the cap level. I have a relic that on use gives me an extra 250 def. this only increases my def chance by 5%. so in total when thats active my def chance is 26%. I don't understand well the whole class and im not saying you are wrong, I'm just trying to get where you pull the numbers from and taken a massive def rating and ignored shield til your 700 rating, which at that point you should have some purples from raids or HM.
As a sin tank I get the feeling other classes don't consider us as proper tanks and only use us as OT since they prefer a powertech or jugg as a MT, so trying to understand what stats i should be looking for in order to maximise my raiding chances.