The glass scratched just as easily tbh. I constantly had to place my 4/4S on soft surfaces to avoid it. Even the tiniest grain of dirt cause the glass to scratch or dent.
Obviously the key difference is that the scratches were only visible under direct light with the glass.
The problem is not flat surfaces but the sharp edge just before the glass begins. Tat sharp edge was rounded in 4 and 4s and made of pure aluminium, this is a coating and sharp thus very prone to scuffs. Nomatter if you put a cover on or keep it naked, a minimum of 1 scratch is pretty much guaranteed the very first week you use it