I had 7000 lb springs supporting 8000 lbs. As soon as I aired up the bags to where the overloads were not fully engaged, my truck would have much more bounce and sway when relying on the bags as the main suspension support.
With my new truck's 13,500 lb rear springs, I have not run it yet with my trailer. So far it is stable with no suspension aids hauling my 4000 lb TC (about 9000 lbs currently on the rear axle).
The air bags on our trucks were designed as supplements to the primary suspension and should not be confused with bags used in big rigs or even a Kelderman setup.