I had airbags on the front of my loosely sprung B2 which carried a 500# Western snow plow in the winter. I have airbags in the back of my FJ Cruiser with which I tow a single axle trailer with a 7,000# axle. My track loader is on it, or right now it has a pallet of pre-mix concrete. The airbags don't lift anything. What they do is inflate into the springs and lock the coils together. You have to inflate them before you put the load on. They work great at that point.
On my school bus I installed an aftermarket air-ride kit. It unhooks the rear mounts of the leaf springs and puts bags under them. They are bags meant to carry a load without the assistance of a coil to keep them together. They are the same bags you see when you look under a modern road tractor. You inflate them and the rear of the bus rises. That's not what coil-helper bags do.