frame flex with anti sway bar

You can soften the springs to keep the frame from flexing. It's really a nonsensical ad to show the Ford frame flexing, but at least it's floor is flat. Take that GM owners. ;)

Seriously though, the system is made up of multiple parts, so change one and you have to adjust something else. If you follow motocross, you'll know that any time they modify the frames, they have to make other suspension changes and relative to a truck, those suspensions have a lot less parts.