The slides are not sagging on any models. They are not going out level, which is a different scenario. Sagging would suggest the slide was too heavy for the rails and/or chassis.
The issue that star chassis is addressing is the flex in the chassis. My 2013 has a lot of flex while driving. It can be torqued with maneuvering and that in turn can make it very difficult to find a good point to extend the slide. The proper methods for doing so are very well documented here (i.e.: check the reveal) and if done properly, all the coaches prior to star (2016) are preferred over the 2016-2017.
The problems with 2016+ are limited to the non-level slide and cracked tiles for the madp and up. The dsdp adds the weight issues to the problems.
I would suggest looking for a 2015 coach.
2019 DSDP 4369 * FREIGHTLINER XCR * HWH ACTIVE AIR
NHSO (Newmar Hoot, Sevierville Original), Kindness Matters