One big reason alone that you will need a WDH is because the receiver is only rated 600 lbs tongue wt. and 6,000 lb tow capacity without a weight distributing hitch. We have an F250 and our TT has a tongue wt. of about 950 lbs. There's absolutely no way I'd tow without one because of the amount of weight that is removed from the steer axle making it far too light and unsafe. I towed our TT for a while without the sway control installed (Reese dual cam arms) and the handling was awful despite having the WDH properly set up. A cargo trailer isn't as tall as a TT and you may get away without sway control.
Do you have any idea what the tongue weight is when the cargo trailer is loaded and ready to tow? You might want to invest in a tongue scale. One problem with flat deck and cargo trailers is that it is easy to load too much weight ahead of or behind it's axles. With a TT, once it's loaded for camping, the tongue wt. doesn't vary a whole lot. A 9,000 lb cargo trailer should have a tongue weight of absolute min. 900 lbs and up to 15 percent, or 1350 lbs is what you want to aim for. Can go a bit higher than 15 percent as long as the truck has the payload capacity.
I've noticed our F250 does sag a bit more than I would expect for the amount of payload it can carry but have never felt the need for air bags. You also want to make sure the trailer is level to slightly nose down and the use of air bags can affect this. I ended having to get a ball with a 1" rise to get from slightly nose up to slightly nose down and it made quite a difference.