They are so bad but it’s just the level of inconsistency despite having so many good players. I believe if a better coach should handle these players they will be more productive than under Ten Hag. I doubt if he is even able to identify the areas that needs to be improved on, he seem confused and at this point I would advise they replace him with a better manager that can lead the team to glory.
I've mentioned times without number that the problem with Chelsea lies on their coach, I feel like he lacked the ability to effectively manage the players at his disposal. I don't think it is true to say that Chelsea lacks the squad depth they require to challenge the status quo but lacks the ability for effective management of those players. We have the likes of Romelu Lukaku who haven't been used effectively yet a lot of money have been spent on his transfer and so on.
Personally, I think the problem is both and indeed yeah the coach is probably the main factor, when the new coach is unable to make all the players into a solid team then the results are not optimal. Apart from that, Chelsea management also has the same role in Chelsea's failures in the last few seasons, they are impatient and want to see instant results while sometimes coaches need more time to change the team for the better.