Why use Elements Unite when you can use Labyrinth builder against Weevil. He is 100% unable to break the wall plus you keep the 500 no-damage points. I recommend switching the skill. Once Master of OZ is out (for Piranhas), you don't need wall anymore. In one turn, Emblem of Awakening, use the wall, tribute Cu for Neo Aqua Mador in atk, sacrifice with white elephant gift. Get 700 points. *Airhorn.
Elements Unite is way better, you get Comeback Victory (500) and Low LP (500), which is already more than the no damage bonus. In addition to that, you'll also get one of the Destroy Monster bonuses for another 100, 200, or 300. You also don't need to farm the Lab Builder drop skill, Elements Unite is unlocked at level 4.
Elements Unite is just overall faster, with more easy/free points.