It is interesting to see how Maresca fits in to the Chelsea project. He was unproven manager that was at Leicester City for one season and took them from the Championship to the Premier League via promotion but never managed in the Premier League himself. If he had stayed at Leicester City, maybe they would not have been relegated. Chelsea took a chance on him and it seems to have been a good appointment as both Maresca and Chelsea have found stability.
For the long term, I think it will never be a successful project unless as any manager (as you put it) has complete control on transfers. He took a big decision by refusing to keep Sterling at the club and the owners backed him therefore he clearly has a lot of control. As for Sterling, his contract runs until June 2027 but Chelsea do not want him back and Arsenal no longer want him on loan. Now the three promoted teams (Leeds United, Burnley and Sunderland) are being linked to him.
What is next for Sterling?

He knew about it before accepting the job; do you know why other experienced managers who were shortlisted left the deal? They were informed what to expect, and they all fled away. You are not allowed to have complete control over who comes and goes; your responsibility is to manage the players at your disposal. The project is dreadful.