I usually rock a case but the face is so big the case makes it bulkier. My spouse was rough housing when it happened. I've hit it by accident since then but no added scratches.
My 2.75 year old Series 5 has never had a screen protector and has no scratches. I have worn mechanicals for years and I suppose I am aware subconsciously not to whack the Watch into walls and hard objects. I have accidentally done this though and never gouged the face thankfully. It’s just carelessness if you do and nothing to do with inferior materials.