Assuming a finite stat pool, you face a zero sum situation with respect to the three secondary defensive statistics. Thus, you stack defense at the expense of stacking either shield or absorb.
The problem with this in the vanguard class is that you waste talents in your skill tree that buff your shield and absorb by adding a percentage of the total. Here are the talents:
Shield Cycler: 2% bonus to shield chance
Ceramic Plating: 4% bonus to absorb
Power Screen: 8% bonus to absorb when fully stacked
Counterattack: 6% bonus to shield chance
Having a low shield chance or absorb means having lower bonuses. This is undeniable regardless of what you may have experienced or what healers may have told you.
I don't think those talents work the way you think they do. They add to your character sheet number, they don't multiply the stats you get from gear.