I'm definitely not worried about this being overpowered. The limitations to mobility (everybody needs to be within 60 feet) and the basic function of the spell (when this is in play, the party's wizard is always going to die first, which is very not ideal) both combine to make it an acceptable option at best. Basically, you prevent the enemy from focus firing but prevent any kind of good tanking from happening, since when the fighter gets hit everybody including the squishies gets hit.

You should specify whether this effect occurs before or after resistances, immunities, and damage reducing effects.