Well the water isn't really pushing them, they are IN the flow of water. We have a lot more mass than water so water could not carry us, unless the water is up to your chest where your lungs are. When they show the waterbenders using a waterwave or even in that gif above of Katara vs Toph, they are seen moving WITH the water and you can't actually see anything pushing on them. If the water was pushing them you'd see water splashing on their backs, propelling them forward. Which is not the case because they are moving with the water and not against it. Even with currents in the ocean, things are able to WITH the currents while moving WITH the water because of a pushing force in the beginning, which is true. But it doesn't equal the same result on land. On land you have the gravity which would push you out of the water in a mid-air wave like the gifs I've shown. The more of your body that's out of the water, the harder it will be for you to stay above the water. I looked at those gifs again and did not see any "ice boards" below their feet. I just think it would require a lot of extra force to keep a body up, out of the water and that force is not being shown. You can't assume that the water is pushing them because there is no disturbance in the water. Once the water goes towards the person and pushes them, it has to go somewhere right? It would most likely swirl back to the end of the wave/spout to cycle again and be a pushing force again. Changing current near the body would result in the entity flipping around, following the current. So how exactly would they be able to just stay perfectly (almost) still? I'm just not seeing the logic, too many factors.