It stopped work for the 5-6 games which lead to his firing, and hasnt worked since, because as a side you are largely one dimension, though Rafa and the players have done well at times. That's what you havent realised, you initially played better under Di matteo, teams worked you out quite quickly, it didnt work for 5-6 games for Di matteo and he got sacked, and every team that has got something from you has played roughly the same way, and Chelsea dont have the answer for it, and you don't have anything different to offer, except maybe a 4-3-3 when Mikel returns.
I'd be saying this of any manager right now, Rafa or not. Whoever has it is in a terrible position relatively, without signings.