This particular claim is getting too deep into the weeds. The calendar favors Djokovic most of the big three, because most events are played on hard courts that are fairly slow ones. It favors Nadal more than Federer, because the clay portion of the season is longer than the grass one, because the hard courts are generally more to Nadal's liking than Federer, and because there are not that many indoor tournaments and no carpet ones. But it favors Djokovic more than Nadal.