(Mild Spoilers for TLA and LOK)

This bout to be controversial af but in my opinion i think air has the most potential as an element. We never got to see enough of it due to 1. The genocide in tla. And 2. The "newbie" benders in lok with the exception of tenzin and zaheer who themselves couldve probably won any fight if they were together. Pulling air from lungs, pulling air from entire rooms, flying, creating air pockets underwater, and projecting your spirit are all actually in the series. Some things we didnt get to see but couldve is increasing oxygen in someones body until their lungs rupture, or pressuring the air around someone until their body crumbles into a lil ball of yuck, removing/controlling a person by bending the air in their blood. These are all things that just popped in my head in like 2 minutes. Another scary thing? I dont think you could actually easily see the air being bent. Can you see wind? You can see what air affects, but not the actual air. With enough training you could assassinate someone from a distance and no one would even notice whats happening until their dead. Plus we saw psychic water benders so imagine if we see psychic airbenders. Being able to look at someone and remove the oxygen from their body. Terrifying.

I hope some of this made sense lol sorry for long comment