I like how everybody ignores the fact that torrents ice sphere can be used as a shield.
Another point I would like to make is, we add this move, what use will it bring, it would only unbalance waterbending.
Here is a fictional scenario with a waterbender fighting an earthbender.
The waterbender uses this move to completely cover the ground in ice, as well as damage the earthbender, the earthbender is semi frozen and while he trys to get to some earth, he is torrented into the water. He is then spammed with a flurry of attacks, while managing to catapult out, but sadly he is dragged back into the water by the same combo that the waterbender used. And is down to 1 heart. The waterbender hits him once with manip and he dies. The earthbender never stood a chance.
I have other scenarios if this one doesn't convince you