Frankly I dont think this impect thing has any relevance to how good teams are. There are much better metrics to measure teams by like, shots on net, possession etc. Ranking teams by how many defenders they beat, that frankly doesn't make much sense to me. By defenders, do they mean any player who is defending ? Is this anywhere on the pitch ? This is all very ambiguous to be honest, I think its actually quite silly. For instance if a team is bunkering, and the opposing team is completely controlling the match, they aren't going to beat very many defenders. That doesn't mean they are a poor team. I think this is a case of bending statistics to mean something which they are not. Statistics can be very misleading, I think that is quite the case with this impect thing.