I have two bikes -- a 2010 and a 2019 Specialized. The latter has the FS 2.0. Both have good wheelsets, with 32mm Roubaix Pro tires run at the same pressure. Fit set-up is the same on both.
The 2019 is very noticeably smoother than the 2010 over rough pavement, square-edged bumps, etc. etc. When riding, one can see the constant movement in the FS -- more or less, depending on where I set the adjustable damping. If I 'lock it out', the ride quality is pretty much the same as that of my 2010, including over the rough/broken stuff.
So, no ... in my experience, the FS is not a gimmick.