I seen some postings of where people at 40 are still getting like 13-15 dmg a tick with radiance.

Is there no way for us to raise the damage of it? :(

Sure. In Seraphim with high PRE, you do about 40% more.
With gravitational polarity, you do another 20% more damage.

Then again, you will lose damage for being in support stance. . . but it fits sooo much better.

Basically, Radiance is a weak damage spell. It is a weak heal. It's benefit and it is a HUGE benefit, is you can gain power either from attacking or healing. I like to be around corners in Stronghold healing my team but not exposed to the enemy's LOS.