I have scratched my Titanium against a brick wall heavily, twice now. The case is starting to look worn, the sapphire looks pristine.I used to rock climb and boulder with my aluminum, which admittedly is a bad idea, but Apple does provide a climbing workout. I would routinely quickly move my hand and grind the glass against the rock face and cut deep grooves in the glass.
I have a Garmin now, but put it away when climbing.
My first Apple Watch was an aluminium. When I learned that I got rashes, I gave it to my wife. A month later the glass looked like crap.