I haul with my truck a lot, and never have any issues. I even have my stock springs removed and replaced with RT springs(~1200 lb payload IIRC) which are then cut for a 1" drop in the rear(about 1.5 coils IIRC), and still have no issues. Here's my truck with maybe 1,200 lb payload in it(on the cut RT springs):
That was on a 2,600 mile trip and it rode fine, not too much squat(even at the limit of my cut springs), plenty of travel left.
My old truck with leaf springs squatted more with the same weight.
I do agree though there is more travel with the coil setup vs the leaf setup. I don't understand why people have an issue with squat though, you are putting weight on a spring, it will squat...