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.
Chelsea have decided on what to do in regards to Sancho and they have decided not to sign him on permanent basis and will pay Manchester United 5m because they will be going against the initial agreement. Sancho will have to look for a club at the end of the season, I believe Manchester United will be willing to sell.