There are too many players there so Chelsea need to make reductions and Pochettino as the new manager there where not as someone involved in buying these players will choose which one he thinks will be suitable as a starting XI and also a reserve so that his team is competitive. Mason Mount has long been rumored to want to leave Chelsea due to dissatisfaction with the wages being earned, with other players still around Chelsea should be able to cover well the place Mason is likely to leave.
Indeed there is a need of making the squad better in this summer. I have talked about a need of a striker only but it isn't the only problem in this team of course. Besides they have actually signed Nkunku for the attacking line which would be a really nice improvement. But I don't know if they are planning to make do with this about striker transfer.
Apart from that I hope another thing not to happen. You know they signed Werner as well from Leipzig but there was no impressive performance left in him after coming to the Premier League. He was a great scorer in the Bundesliga. I hope the situation with Nkunku doesn't become similar to that as well.