Disagree about your first paragraph, it is definitely your opinion and assumption rather than Mourinho thinking. He is dropping Oscar and choose Fabregas instead as no 10, mainly against attacking teams when away, because Jose basically want to put more players in midfield to hold the ball and easily build the counter from there. Fabregas playing more deep most of the time, only when we attack or counter he then play as no 10. Yes, Fabregas is more fit to execute that role than Oscar, no one will deny this. Oscar still in Jose plan, because against defending or inferior teams, Oscar style of play more suited as our no 10.