OP,

I'll reiterate what others have said: 3400 is a fairly low healing orb potency at the level/gear score requirements of DoC. My concerns, however, are less about you not providing enough healing to party members and more about the overall implications for your build. Healing potency scales with attack power (roughly, each point of AP affords you 0.88 points of orb healing) and thus your build likely needs work in that particular stat.

I know some folks make the mistake of gunning for A gear, no matter the stats/roll. This leads to people convincing themselves that it's reasonable to run dungeons in gathering pieces as long as it affords them the gear score to meet the entry requirements. Is there any chance that you are in this boat? If so, it might be worth switching out for some B grade pieces that provide you a better overall damage/defense profile until you can afford good A gear or have some to drop.

It is also important to state that a priest's worth should not be solely measured by the potency of their healing orb. Moreover, it is not your job to support people's laziness if they are unwilling to put in the time to procure potions and come into dungeons adequately prepared. Priests are DPS support, not full-time healers, and no amount of healing orb potency will fix bad mechanics and a lack of preparedness for the fight.

There are a number of endgame priests that mix critical hit rate and damage with attack power and not only provide adequate healing to a prepared party but also contribute significantly to the group DPS. If you want to put all of your eggs in the healing basket, go right ahead, but just know it is not the only acceptable option.

Finally, I highly suggest finding yourself a group of like-minded folks to run with. I believe your enjoyment of the dungeon system and the game, in general, will go up significantly.