Too mobile for Earth... Although, it is not like like somebody care by this my remark, since they want to keep waterbenders
too mobile on land (like wtf? Bias much
@Loony). I do feel like it would be neat If an earthbender could create a hole below themselves (on others) with the via collapse left click. The Idea of "like fast swim" speaks for itself that it makes a rip-off from another element and that's why it ain't unique--
And yeah, while Air&Water Spout abilities contradict my point, those two are a valid exceptions because they are canon and provide a balance mobility in their respective enviroment. TBH, I think the canon part is important and its quantity of how many times this suggested combo technique was shown, and If my memory serves me well: I'd say the number is weak.
The Concept of earthbending is to be rooted to the ground, and be like the rock:
unmovable. Which is why this bend art is opposite to air, which nomads often utilize "avoid and evade" as they're pacifists. Even toph stressed it out to aang during their training. If we give them this combo, than it is unbalance element.
And I'm NOT saying earthbending as of right right is perfect on its mobile side (thought that isn't only, but that 'll be for another talk), but your given would just worsen it more. Like hello, earthsmash can friken fly the user helicopter fashion.... like FLY???!?
. That's not how it was portrayed in the show, and it doesn't make sense, since it creates the Carry-yourself-by-pulling-rope-from-you paradox.