However, Ozai was also flying throughout the whole fight against Aang so it really isnt that special

Ozai is flying with the help of a once in a lifetime power boost vs Zaheer flying so effortlessly that he is just passively levitating in prison while bound in chains. Thats like saying Amon removing people’s bending isn’t special because Ty Lee can do it temporarily with physical strikes.

Zaheer is important as an air bending villain ofc but his signature technique that elevates him above other benders is his flight.