Pokemon World Championships is pure garbage
The second battle was actually far from being ok, especially when it wasn't drawn out enough, which a rematch like that should've been especially where Marowak is supposed to get its revenge for its previous. This is despite the fact that at the time of the start of the second battle, there was more than enough screen time left in that episode to make the battle more drawn out and giving it more screen time. And lastly, Rain Dance was basically a pointless move in that battle as it literally served no purpose.
I agree that it felt rushed but still the battle served its main purpose. Personally, I didn't mind that much that the battle was short since we already knew or more like it was obvious how the battle will conclude. Regarding Rain Dance's presence I guess it was a strategy to weaken Marowak's Fire-type attacks and probably to give out a more dramatic atmosphere during the battle's climax.