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The transfer window is still open, and because both coaches are experienced, they will know whether or not to sign fresh players for the following season after selling some of them to other clubs. Teams who sell players do so due of the manager's decision; if those players cannot fit into the pattern of football they want to play, they easily release them and use the ones that are available, or better yet, look for better replacements for them. If they've been doing well even after selling some players, they should be able to do the same when the regular season begins.
The problem is not about regenerating players every season on a regular basis, but that some teams always have difficulty realizing their coach's wishes to recruit the players they are targeting. I believe Pochettino, Ten Hag, Klopp, Arteta and Pep Guardiola have a roster that they are looking at, but that realization may be too difficult because a lot of players have been up-priced by their owning teams.
Coaches will make adjustments based on their needs and plans, that includes who they need and who they don't. Chelsea is the team that has been the most aggressive in recruiting new players, they have also sold the most players who are not included in Pochettino's plans for next season.
Yet the players recruited aren't worth winning them the top four positions this season. They have quality winger's but the midfielder's in exception of Enzo Fernandez are not qualified for Chelsea. I also doubt Pochetino would do a great job for Chelsea. It would sound stupid but Brighton current head coach would have done a better job for Chelsea to Pochetino.
Chelsea has got to sign Caicedo from Brighton and also Kudus from Ajax to make the midfielder's solid else they're going nowhere.
Declan Rice is a good example of overpriced players this season. He's tough and solid but the fee is way too high for Declan Rice. He was effective helping West Ham winning the Conference Cup. He has all it takes to settle down with the gunner's.