the shell material is heavier on the non-s-works version, and as you note, titanium vs carbon rails. The 1.7 ounce difference is not significant for an eBike.
right, it’s some kind of nylon - carbon composite. you can tell in the photos on the specialized website that it’s slightly different.
i have the s-works one on both my road bikes - the pro / slightly less expensive version wasn’t available at the time i got it. i have around 10,000 miles on them now.