This is a good point. I agree, Transmutation would be the correct school.
And another good point. What's the source for master air anyway?An additional thing on the perceived power, you should compare the spell to Master Air, the 2nd level Druid spell that gives flight for rounds/level. No self-respecting Druid bothers with Swift Fly when they have that. Considering a Pally is only getting 1 or 2 spells at 4th, getting 1 round of flight (CL 1, remember?) isn't breaking the bank when the full casters are throwing around fire and holy smitings of their own.