Accusing a player of being sluggish or playing poorly is simple although there are situations when timing and fit are the only elements at play. Even though Sancho wasn't the ideal fit for Chelsea's current requirements. He is still a talented player. For a number of reasons, clubs move on, so Chelsea would be prudent to rethink their choices if they believe they can find higher value elsewhere.
I believe Chelsea has already calculated properly about Sancho's contribution to the club. They feel he's not good enough. That's why they decide to part ways with him, and none should be blamed here. Sancho is a talented player, but not good enough to stay at Chelsea. They wanted more than him who can actively scored, and contributed a lot to the squad.
Wasting 25 million for him is just another mistake. His salary is also quite high, which is not worthy to keep.