More than 5% OM is my indicator of soil chemistry and nutritional issues. Think grass that has been growing and dying on itself 365 days for maybe decades, yet soil pH, base ratios, and nitrogen content of the vegetation are not conducive to decomposition. I do the unthinkable, I do not collect clippings on my reel cut lawns. Thing is, in about a month, I cannot recognize them as clippings. Conversely, a common renovation procedure around here is to scalp a lawn to the point that you can see dirt and then verticut the H-L out of that lawn, picking up whatever comes to the surface. That is a good way to remove the excess organic matter. Those in the know either do not apply anything other than an inorganic fertilizer or silica or washed dune sand as a top dressing. I start fertilizing and addressing soil chemistry after scalping. The ones who really need to think about what they are doing put organic matter on a lawn where several cubic yards of it was just stripped off.