I would like to state that the first very problem Chelsea had last season was having a big squad with too many players..
You are kind of right, they spent lots of money last season getting players, but its not all about having big squad but the players should be ready to work for the club. See the way Arsenal performed well last season and most of the players in the club are young player, but from their performance, you will see that those players are ready to play for the club. I think Chelsea needs young and talented players, its not all about getting big players, but getting players that are ready to play for the club.
Tuchel who had the control was sacked and a new coach came in, for an amateur but good coach like potter, a team with so much size would be a problem!!!
Right from beginning i knew Chelsea's, problem is not from the coach but from the squad, Tuchel was a talented coach, and since they sacked him, things have being getting worst for Chelsea, but lets hope we see a positive result from Chelsea with their new coach.