Overskim is a term used loosely. It's all relative to bioload, feeding, and nutrient content of your reef. Yes it is possible to overskim, but it's also possible to under feed, under stock, overdose carbon sources and chemical media, and do too many water changes. The end result is all the same; a stripped system with corals that appear starved and faded in color.
Also, it's hard to go by skimmer ratings since most if not all brands overrate their products. Try to search a system similar system using the same skimmer if possible to see their result.