the cool nights can chill the brood. they currently are "used to the insulation" by removing it you are creating change.
IMO the insulation did not cause the sugar to be eaten, the hives lack of honeys stores did.
Robust is good, why try to dampen it. 1000 years ago in a tree, the 3-5 inches of wood...... did not get taken down to 1 inch for the "summer" Me Thinks you are over thinking it.