The way I see it there are no real purists in the strictest sense. Obviously some are more than others. Even the uber purist Wenger has adapted and based on this season and not on his entire tenure they do play differently. Its less expansive and more willing to grind, for large spell while they were at the top of the league it wasn't freeflowing and more defensive than the typical Arsenal we've become accustomed with. If you look only at the game against Tottenham, they were pleased to sit back and hold the lead. Once people are classified in one group it seems very difficult to break free from it. Another of the so called purist in Rodgers has transformed liverpool for the better by moving away from his usual pass to death style he had at Swansea to a more counter attacking style. So it has to be ever changing and tinkering otherwise you will be left behind.
It will be interesting to see what will happen at Chelsea come the summer, if we solve our strikers issue by signing one world class forward and bring back lukaku potentially would Mourinho revert back to a more possesion based game? Personally I would hope not. If I remember it was the Sunderland defeat in the Capital One cup that prompted Jose to change back to a more pragmatic approach. We've got a quite a summer in store for us Chelsea fans one way or the other.