My guess is you are not optimizing your gear properly. Rakata mod-optimized gear should do better than that.
For your Mods, you want to get the ones with the lowest endurance and a balance of power/willpower. If you use power crystals, you will need a few mods with low endurance willpower/crit.
For Enhancements, Power/Surge is a good one. Make sure it's the low endurance ones. A few of the enhancements will need to be power/alacrity so you don't use too much surge above the diminishing returns cap.
The advice I posted way back
on sorc stats still holds true mostly. War Hero relics of boundless ages are not too hard to get and yet are right up there with the best in slot items.
For augments, you want all willpower. Power is almost as good point-for-point as willpower for healing, but very slightly behind because willpower also affects your crit rating and has a seperate diminishing returns forumla from crit rating.
So long story short 1.5 numbers look like this:
Get your crit/surge to about 250 or so, willpower/power as high as possible (as long as endurance is as LOW as possible on every mod/enhancement/armoring).
My sorc's power is 1k, crit 210, surge is 280, alacrity 281. When my AOE heal crits, it hits for about 900. Without a crit it's 530.
Note that I don't mention "force power" which comes from the hilt on your mainhand and offhand. A good hilt (at least rakata level) will help.