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.
Earth is balanced by having two advanced forms, fire and water only have lightning and blood bending respectively. Earth has metal and lava both, though even if a bender is capable of either they only get one.
I always felt that air kind of got ripped off by not having any kind of advanced form but occasionally they just learned to fly so I guess that's pretty unique and powerful.
I always forget about combustion bending because of how rare it was.
Ice is just frozen water so idk if it should really count. Healing is a nice benefit but water is also the least likely element to be around unless you live near a major body of it.
Water bending is objectively the scarcest element and specifically why they settle at the poles where construction with ice is simple. That's why they have so many benefits like healing and being overpowered with blood bending.
Air and fire are at will, and earth exists wherever humans live since we aren't aquatic. Water definitely has to plan for not being near water, no one else really has to do that kind of a thing.
Now that I think about it, any of the kids could do much more with their power. Fine, "heart" can control animals. But then we have earthquakes, hurricanes, tsunamis and whatever flamey shit fire can do. Basically if we drop the limitations of the user not willing to go all out, they all get buffed and "heart" still sounds underpowered. Unless it can control human minds too, now we're talking!
There was a "power glove" episode that did this i think? It gave whichever ring bearer who had it like 100x power with their ring. Of course it was evil, and i want to say it was mai tai and the "heart" ring that won the day, but I can't be assed to find the episode to make sure.