Chelsea did spend too much money last season to bring in all the talented young players and they shouldn't have to be hasty in making these purchases if in the end Chelsea change coaches for one season. Now Pochettino's arrival will indeed give a new color to Chelsea and of course, as you said, every coach will only need players who are felt to meet the standard strategy that he will provide.
Chelsea's mistakes are indeed very difficult to accept and therefore now the players will start to be sold in the summer. Regarding Mason Mount, it seems that he is not comfortable at Chelsea and the salary does not seem to make him want to stay at Chelsea. There will be many replacements for Mount later and Chelsea don't seem too bothered by that.
What I see is that they buy players based on their likes and not based on the abilities of the players they need, so that makes buying their players look like a waste and not contributing to the team. Indeed, they should make an overhaul in their squad and start sorting out the players they will keep and also start looking at which players they will bring in for next season.
They have to lay the groundwork from scratch, because this season they are so messy and it's impossible to continue. If not then they will probably feel the same way this season. There is still time for them to build a solid foundation.
Todd Boehly take over started this mess-up here in Chelsea as he bought 17 players first under Thomas Tuchel and then Graham Potter but both time his interference create problems and both coaches sacked now third full time coach is arrived, and they need to sell few players immediately which bring some positive things even mostly players were well known in UEFA clubs, but still results were not as par requirement because coaches fail to set winning unit which was main issue now they need to start from scratch and also have to allow coach to do things by his own instead of interference by management because this will bring stability and better results.
Hopefully now new coach will be done better things and try to set players which will give him better results many are already going to be listed even this is going to be lost for them because now mostly players are having decline into their market value, but this is important for the rebuilt.