I see what you're saying, but the fact is that Fire has most of its moves devoted to offense. Like in the anime, it is primarily "the best defense is a good offense" and that's fine, and pretty effective. On the other hand, air has two (three if you count airsweep) damaging abilities, and is primarily defensive. So, logically, it stands to reason that its defense should be the best, and the fact is that Earth currently wins hands down with earthwall. Now I'm not suggesting a totally OP version of what it is now, I am suggesting a more dynamic version that cannot be used to camp, but actually works on moves besides fire projectiles.
Also, for MY two cents, i would say that fireshield could do with some improvement too, but that's for another thread.
Thanks anyway for the contribution.