I think the problem of recent years doesnยดt only lies in the defence.The midfield of the top 6 Club from the 2000ยดs until 2011 there were only the best midfield players at the likes of Chelsea (Lamps in his prime,Ballack,Maka,Essien..),United (Scholes,Hargreaves..),Arsenal (Fabregas,Viera,Pires..)or even Liverpool (Gerrard in his prime,Alonso..).4-3-3 was often the formation,in which the teams excelled at this time with three class midfielders,who gave the teams stability and goals (LAMPARD!!).But then the teams changed their concentration from the center of the field to the wings and hired as many good wingers as they could and ignored their stability in midfield.So got results in top-games like 8-2 or 6-0 or 4-0 a possibility and you can count atleast 5 such games in a single PL season,which was unthinkable in 2007 for example.