Chelsea have the history of winning the Champions League in the condition of the team not going well in the English League, but this season cannot be used as a reference that Chelsea can repeat the same thing. The midfield is indeed quite crucial because it is the brain of a series of attacks that are trying to be built and if the attack line is creative enough in building attacks it will be easier for strikers to score goals. Of course all crucial positions in football and I don't think Chelsea have not lacked good players, it's just that so far it has not been fully maximized in contributing to the team.
Chelsea have made quite a number of changes to their squad from last season, it is normal that after making many changes that they team will need time to play together and build good team chemistry so I think Chelsea are currently lacking that connection between the players especially the incomings. Let?s see how quickly and well they can blend in and make maximum impact this season.
Many times new arrivals change the fate of a team because they don't find much affinity with each other, but I have to say that there are many players who, once in the team, manage to do very well and have fun and make others have fun and play well with their teammates too, so it's not a given that they don't get along well with each other.