That is a falacy. The round on ejection doesn't slide over the breech face it is kicked strait out by the ejector pin. It does slide on the breech face as it is being stripped out of the magazine. What you are seeing is shavings from the case rim as it catches on the firing pin hole. A simple deburr tool will remove the sharp edge of the firing pin hole. Don't over do it. Just get the sharp edge off.
Um, not exactly correct. With a blow-back operated pistol your statement applies, however the Micro 9 is a locked breech design.
With a LB design, the round remains in contact with breech face while the barrel is moving downward during unlock while dragging the round with it.