It would be too oP if your allowed to shoot through bubble. There should be a downside to this like you'll deal less damage when shooting through bubble. As for the damage buff there's no need for it. Defender is built for defense not offense so instead of weapons of light. Give it armor of light. In the end of the day your sacrificing offense for defence.
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Defense isn't necessary. At least in the way Ward of Dawn currently does it your standard Tower Barrier does that better and you can run sunbreaker for melting point. It needs a damage buff to see actual use.