I would actually agree with that. That's canon alright! Though it's more to do with IceWave combo than waterwave.
I'm not sure how this would fix anything... By "On land" I'm sure he means plants, which means still taking more water from plants than they actually have.
I think a couple changes could take place to better help water on land. For 1, there needs to be less "water disappearing" If you don't have bottles all of the water moves you shot just disappear. Instead, they could fall to the ground as little puddles, the smallest size of water source as you can have sit stationary would be nice. Then with any water move that requires shifting, it will check for any source of water puddles to make the move. For instance, you fight someone with Water Manipulation on land using the local plant life. Instead of the blasts disappearing, they fall the the ground in small puddles. Then, when you're low on health, you need to make your escape. You hold shift using Water Spout and it then starts to extract the water from 3-4 of the near by puddles.
Another way would be plants. Just like the puddles, each move requires a certain amount of plants near by to work. I have no doubt this has been suggested before but I'll mention it anyways. When using a water move when plants are your only source, you'll need a certain amount of plant sources near by for it to work at all. Water manipulation would require 1 source, water spout Wave would require 3-4 sources, torrent would require 3-4 sources, etc. And then for ice moves, they must first he extracted from the plant as water and then VISIBLY turn into the ice move used. For example, when you shift+click using Ice Spike (which would require 1 source), it first comes out as water than we see it turn into ice on probably the 3-4 from of the animation.
Just some thoughts to debate about.