Yes, I got two micro scratches on my device very quickly despite babying the device. Essentially if you are anywhere in a sandy environment or exposed to sand/grit - that's the main culprit to watch out for.
Gorilla Glass 4 may be able to survive keys, knives and whatever else, but it's the smallest inconspicuous little sand and grit particles rubbing against the screen that cause damage.
If your in the city or an urban environment you may be fine. If your on the coast and exposed regularly to beaches, then use a screen protector and great caution.
Like yourself I have tried these curved glass protectors and the corners raise with a case and even lift a little in the middle of the screen reducing sensitivity.
I now have a film fitted both front and back and its a much better solution IMO even though it seems to have an almost soft rubbery properties its smooth to the normal touch stokes although slightly harder to clean.
Living on the edge of a desert I agree unless there is a 100% sealed contact there's always the chance of trapped grit/sand
I noticed in one of your other posts you noted that you cut the corners off the protector, I'm surprised as I thought being glass it would crack at the very least