It is perfectly normal blade wear
Of the blades I replace around 90% of them are due to the flutes breaking off
Of all of the spindle bearings I replace at least 50% are due to continuing to use the mower with the flutes broken off .
What you think is in your soil and what is actually in your grass are two totally different things
Normal enviromental dust will be deposited on you grass on a daily basis
The grass itself will make an erosion grove in the blades despite the fact that grass is soft & the blades are very hard .
Water is very soft but it made the Grand Canyon , over time it wears out the outlet holes on sprinklers & hose nozels .