Sure, it's not a solution that will scale. As is wind energy: if we cover all the oceans with it, it will influence our climate and probably slow down the rotation of the earth, etc. The point is that a relatively small such storage plant can already store a huge amount of energy - enough to help balance a lot of offshore wind.

Very funny.

You are aware, are you not, that there is 3x as much sea floor as land?

And raising the sea level would take more air than has ever been breathed by the entire taxon of primates. You would never store more air than needed for a day or two of power generation.