I ordered two of this product as well (one for me, one for my GF) as the scratch test video with 9H pencil they posted seemed promising. They cost me almost $100 for two of them incl. shipping to my country (I live in asia).
I was worried about the product's chemical/oil/water resistant properties so I actually wrote them an email asking if daily exposure to water/soap/oil on the skin could damage the coating.
Well, the answer was no and they seemed pretty confident that once the coating has settled, it is unlikely that water could wash off the coating. They told me that their Onyx coating is waterproof and chemical resistant so they would withstand day to day exposure to moisture, oil and such without being damaged.
Which led me to believe that your coating might not have broken down or washed off from oil/moisture on your hands as you claimed. Maybe possible in six months, but I don't think that it can happen in just two days of daily usage - provided that you believe in what they're saying.
I suspect that the coating - not the phone's finish itself - is what had been damaged to show the micro abrasions you saw on the phone, which must have come from some sort of a quartz-based grain of sand or dust.
Also, that the coating withstands a stroke from 9H pencil does not mean it has a *Mohs hardness scale* of 9. A 9H pencil is on around 5-6 of Mohs hardness scale, so I'd say the coating must be at least harder than that, but not super harder. Realistically, I suppose the coating's hardness would be around 6 or 6.5.
On the brighter side, that puts your Onyx coated back plate to be almost as resistant as the gorilla glass on the screen(hardness 6.5-7). Might not seem to be much, but that is a whole lot harder than its original aluminium surface, which has a hardness rating of 2.5.
TL;DR: The Onyx-coated Jet Black finish won't be impervious to damage, but hopefully it would retain much less scratches than it would without the coating.
