Question about Garmin Fenix 6 Sapphire

On the product description at Garmin you can see that the metal of this model is DLC coated (which has little to do with the glass, but is not needed there). I have been wearing it around the clock for almost 2 years now and often use it on outdoor tours etc. and apart from hardly any visible signs of use, it is like new. Except for the quality of the wristband (which can be replaced), everything is top notch.

When I look at the specifications, it says stainless steel, titanium, DLC coated

Sapphire glass is not actually glass but a synthetic sapphire and therefore many times harder than any coated glass.
Coating sapphires therefore makes no sense at all.