In theory I'd say a priest is much better than a shaman for healing 4 warlocks. Real aoe healing of nine targets, even with an instant cast, instead of ghetto aoe healing of three. That alone is a huge difference. It is also nice being undead.

If max melee range is 3 yards and minimum ranged range is 4 yards, thats a 1 yard deadzone. Thats 1/3 the size of the current 3 yards(5 yard melee, 8 yard range).