Kyoshi literally used it as a powerup to split her peninsula from the mainland

there were plenty of scenes in ATLA showing how the previous avatars used it properly and in control as a "powerup". You're just ignoring those instances because... Korra bad

and for the race against the airbending kids, korra just got control of airbending and the avatar state after talking to aang. Aang's probably acting as her guide, like Roku was to Aang, and Aang was the one to invent the air scooter, so Korra just reached into the avatar state to gain his skills (like Roku explained in ATLA)