Since I have this set up on my Guild's website and don't want to reformat it for here, check this link - For anyone who wants to know the in's and out's of tanking with Vanguard for PvE - Flashpoints, Heroics, Operations, etc.
Nice guide and oddly enough you seem to spec your VG the same way as mine.
And i agree that for the VG defense is for the most part useless (ya i said it lol). It just costs to much for the VG class to stack in my opinion.
P.S. Another reason I like ignoring defense is because of the skill bonuses we get from shielding an attack. I also believe higher shield results in less chance of being crit.
For example when fighting a mob the first roll goes against your chance to outright defend it (dodge). After that it rolls against your shield chance. It is my theory that this roll also goes with chance to be crit (crits can't be shielded). Thus if looking at a 1-100 roll having a higher shield lowers that chance to be crit and thus a mitigated (aka shielded attack) will commence.
Example being say your shield is 50%. The mob roll for crit i believe works the same way as defense and thus has a 1- 50 chance to roll a crit and ignore your shield. The higher your shield the less likely you are to be crit by a physical attack. So at 60% shield the mob has a 1 - 40 chance to roll a crit attack. Otherwise it hits your shield and thus also your absorb. Granted some attacks (force/tech) ignore shield all together but 80% of most boss mob attacks can be shielded. Thus in theory the higher your shield the less chance you have of it being ignored. VG's get a bonus to absorb and shield unlike our force using counterparts (they get def bonus). So why not roll with being the meat shield.
Another example is HM Esseles. The final sith boss hits me for 99 dmg. The only time he ever hits me for any decent amount is with force choke (unshielded attack) or if he happens to land a melee crit (fairly rare). Otherwise it's 99 to 104 hps worth of dmg each time.