My family used the Synthesis case for their 8 Pluses and it is holding well. While it wasn't the best comparison, I compared the iPhone XR Sheath to the Apple leather and silicone case for the iPhone XS Max. They are equally thin, which is impressive because the Sheath is rated for 6.6 ft drops. As far as I know, the official Apple cases do not have a drop rating.
Definitely more of a hard plastic feeling. The entire case is textured for grip. If you ever used the Silk base grip case, the feeling is very similar. The drop rating is 6.6 feet, which is head height for most people.