I have commented several times that, if you want to fill your deed log, The Lord of the Rings Online™ expects you to run each instance six times. You can tell this by comparing the deed amounts to the number of enemies in the instance.
This is reasonable given that you have a team of six, with one drop at the end. If your team runs one of the hard mode instances six times, everyone has the radiance piece. Surprise, you also get the associated slayer deed. It is a reason to stick around and help others, although it does mean you are committing a solid day of your life to some instances.
This is less reasonable for the three-person instances, but old habits die hard, and they are pretty quick anyway.