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.
The coach will be the first person to blame when a team fails to perform well, but we also have to see how Chelsea management always makes hasty decisions regarding their coach. The reason is that they don't give the coach much time, in fact they only give the coach one season and then they fire him.
Many teams fail in their first season with their coach, but in their second season many finally make good progress and now Chelsea is not doing that.
Pochettino, for example, had to be fired at the end of this season, even though in terms of his game I think he could show progress, Chelsea were not satisfied so they fired him. It is very difficult for a coach if he is only given a very short time.