It's possible that they decided to make the sport class more impact resistant with the tradeoff of being more scratch prone, but I'm not sure. It did seem like the newer phones did the same. Lots of people feel like the X and XS scratch easier than previous models. Thats the thing with glass, you have to pick which side you want, you can never have both. Thats why sapphire, while being awesome at resisting scratches, will shatter on impacts where the sport won't.
Kinda on the fence with this, i wanted SS for the saphire glass, but since the S2/S3 i see lots of examples of scratched Saphire glass, the Ion-x glass is super sensitive to scratches, my iphone 6 plus is a living example.
On a device thats facing outwards all day long vs a phone in my pocket, i need the best glass to prevent it from being completely wrecked a year later.
On the otherhand the SS model is around 40% more expensive, i could easily put that money forward for next years AW5 instead and just do a yearly upgrade and live with scratches/ screen protector on the Alloy version.
Just to clarify, the back of your Apple Watch was scratched by a black Milanese loop band Due to the DLC Coating in the thread you started, this is referring to those with scratched displays, in this case, the OP has a Sport model.
More to the point:
I was never impressedwith the Ion – X Glass on the sport model. Mine also scratched easily when I first purchased the Apple Watch Sport, and then I upgraded to the stainless with the sapphire display, never had an issue from that point forward.