A few ways to make it less cool and more "umm, okay".

1. Can't fly up during combat.

2. Flying up takes more movement than for air forms.

3. Moving around takes lots of move and has lag.

4. Each tick in the air costs non-insignificant move.

5. Can only see what's below you like minor air forms can.

6. Flyto has lag. Maybe like a 1-person tess. Enough for someone to quaff, blackjack, cast sleep, etc.

7. You can't do anything combat-related in the air, e.g. parry, dodge, shield block, cast, sing, commune, etc.

8. All major air forms are faster than you, i.e. one hits you and you're dead meat.

One issue with making it expensive movement-wise is that low-ranking arials would literally start dropping like flies.