I don't have any experience with a child that old developing asthma, but I do have LOTS of experience with asthma. My daughter is now 5, but was diagnosed with asthma at 3 months. Until she was almost 4, she was on the following med schedule:
Inhaled steroid (pulmocort first then Qvar as she got a bit older) morning and night.
Singulair 5 mg nightly
Zantac morning and night
Aerosol treatments (first accuneb, then albuterol, then through 3 different doses of Xopenex) every 3-4 hours on bad days
Plus a Xopenex inhaler to use as needed when she gets an "out of the blue" flare up.
If he is seeing a pulmonologist, and he is getting better since he has been medicated, leave him on the meds as directed by the pulmonologist. The reason he is doing better is because of the meds that he is on. The Advair and the Singulair are controller meds. These are medicines that work in the same way as some medicines do for those who have high blood pressure or diabetes. They help to keep the body balanced and functioning the way it should be.
The Albuterol inhaler is meant to give his airways a boost when he exercises or plays real hard. Taking it before hand allows it to fully penetrate the airways while they are relaxed as it is very hard to penetrate them when they are already inflamed.
Because he is on Flonase, I'm going to go out on a limb and guess that he may have a bit of allergy induced asthma. My daughter was on Zantac because she had a very small problem with acid reflux which really aggrivated her asthma. The point is that there are often times when outside illness/disease will contribute to asthma.
Sorry to be so long, but I do feel almost like an "expert" when it comes to asthma because I have dealt with so many ups and downs in such a short period of time.