Suggestions on how to make it better. Lower the damage reduction by the number of people in it, or apply the damage reduction to the X lowest health people where X is a small number.
For reference, the latest patch note from beta.
Power Word: Barrier duration reduced to 10 sec, down from 25 sec. No longer absorbs a given amount of damage, now reduces all damage done to friendly targets by 30%. While within the barrier, spellcasting will not be interrupted by damage.