Don't think it's changing the defenders, more likely replacing midfielders. Who in previous years wouldn't have been able to track back later in gamesHas 5 subs mads a difference this season ? able to throw on fresh defenders ?
Opposition can put on more attacking players too, but guess they won't in general be the top quality ones ?
I think the fact that on the whole players are fitter and faster than they used to be so more able to get back and defend , or can break faster from defense means in general its much less common for teams to get attackers outnumbering defenders very often in games