Whats your problem with the screenshot? The sage wasnt far off the trooper in healing, plus he did more damage aswell. To make things clear for you, once you pick the healer advanced class, youre not really "tanky" anymore. I am not playing trooper but bh and both advanced classes at that, and I can tell you that even the "tank" advanced class is not really tanky anymore once you spec for dps in that.
The healing advanced classes on trooper and bh get no shield generator and no talents to boost up shield chance or even make use of them. You will get around 30% armor from good gear, versus a real tank that is also tank specced will get 50-55% in good gear. The real damage mitigation mostly comes from not only the armor rating but from stacking shield chance and absorption and adding a bit of defense rating aswell. You can get around 45% shield chance and 50% absoption relatively easy, in pvp gear it might add a bit more shield chance but less absorption, this means you can add around 25% more mitigation to the normal defense. But this only applies to the vanguard and powertech advanced classes, not the healing types.
Trooper and bh healers get the 25-30% armor and that is it. They dont have the defense stance that boosts their defense ratings by 60%, nor can they make use of shield generators.