One of the reasons why clubs like Chelsea is currently struggling as is because of the kind of players that they have signed in the past and that includes signing of players that are still in their teenage or developmental stages of their career as these players can't be used in challenging for a trophy because they don't have the mindset and stamina to do that what Chelsea needs currently are world class players that are ready made and can challenge for the league and help Chelsea finish in a good place in the league
If Chelsea are still signing young players it shows that they have not still learned from their past mistakes and history will likely repeat it self as they will struggle because these players can't produce results that will really put the club in a position that will be helpful to the betterment of the club
I don't feel Chelsea are currently struggling at the moment, they have all it takes to make the team one of the deadliest team in the EPL but it seems they have poor management, fine they signed lots of players and more teenagers but haven't you seen how some coaches transformed those guys who have no experience to a weapon for the club? To me from the number of players Chelsea have signed I don't think they need already made players to do better or make them win trophies, they have it all. And check the table they are doing well just that they lack that number 9 man who would convert every opportunity and you don't expect a team without a striker to always win games and get more goals, things like that only happens by a slim luck on their side.
Instead of signing is better to build the team with all they have not by discarding the important players and settle for the ones with the ability to make more mistakes. The manager don't know his first 11, when you look at the back line he is not ready to make 1 or 2 players to be the leader to control those guys with poor mentality, every game he switches players and it makes them to lack that understanding, a team like Liverpool have Virgil van Dijk and Ibrahima Konaté, they have a perfect understanding and partnership even when they sub Ibrahima Konaté for Gomes the understanding is still there but for Chelsea nothing to say about them in that department.