I think you do not understand my statement. I never mean defensive mentality leads to low number of goal conceded and scored in a season. I actually mean that I will tend to use harder defense mentality to lower score margin in particular match, and usually turn to attacking mentality at a suitable time within a match to try to score.
But I agree your observation. My teams start matches with defense or hard defensive mentality in all season but one of my players usually obtain the best scorer title every season.