I'm not sure exactly what's going on with either stem but I've used a variety of cheap and high end stems and not had an issue with slippage.

The issue with scarring as a means of generating grip is that you are hoping those scars transfer over to the stem. That's the only way they generate any increase in friction. In my experience, this will be a short lived victory. The better approach is to work towards getting full circumferential contact between the stem and steerer which, if my assumptions are correct about the bore in your stems, will require some sort of shim.

Any chance you could send me one, or both, of the offending stems and I'll do inspection to sort out where things are going wrong? Then hopefully I can return the stem(s) with a properly sized shim.