Every E-Series vehicle has had a FRONT anti-sway bar since the 1980's if not before then. The E-450's have always had a REAR anti-sway bar also, and Ford started putting them on E-350 DRW Cutaways a few years ago. These OEM bars have been found wanting by many RVers, leading us to remove them and install much bigger/stiffer ones from vendors like Hellwig and Roadmaster.
The way I read Jayco's claim that "no other C has it" is that they are upgrading their C's with one of the aftermarket bars, as well as upgrading shocks to Bilstein and adding Hellwig helper springs.
Jayco is doing something many of us have already done, but I choose to applaud them for at least doing that very something. The one that should be doing that and more is FORD. The claim that Ford makes that they can't provide upgraded components because they don't know how the chassis will be used is RUBBISH. The chassis the RV builders buy is a version of the E-Series called (guess what?) "RV Prep."