But, it gets no boosts, like the moon or the sun being stronger. Earth also gets no boosts, but it’s balanced by offensive power, whereas Air is a defensive element.
As far as space travel goes, if any benders were involved at all, they’d have to be a team in close concert, because any one of them holds the power to kill everyone on the ship.
But, if they decide to continue the story in that way, I would be 100% down to watch that.