There is a lot that Chelsea needs to improve, not only in terms of recruiting players, they have spent a lot of money to buy players at high prices but the fact is that Chelsea has played badly in the last two seasons. Oshimen is indeed a talented player, but if he is not supported by his teammates, Oshimen still cannot bring Chelsea success alone. Cooperation between teams and the tactics provided by the coach are very important for the success of the team itself.
I like and agree very much with your closing statements, team work is always something that can't be over looked when checking out a teams performance, if they have got a good team work they will literally be very strong enough to handle almost every team they literally come across, a typical example has to be with Leverkusen, they have got an awesome team play style and that has helped them achieve so much already this season.
If Chelsea works on their team work strength and their abilities to be able to tactical harness their rhythm while using a good team play, their results will be such that they will be really proud of because the team actually is got a good form and depth so they actually don't necessarily need recruiting too Many new team mates but strategic positions can be replaced with new good players while encouraging team play amongst them because even if they have got good players and no good team play amongst them, they will still not make a good team.
Next season is a good opportunity for Chelsea to figure out their form and pit it in other and they can dare to win a trophy, so they have now till next season to fix the team right and not having to wait till it's next season already before they will be able to do that as they may still have to suffer the same fate they have suffered for over two seasons now. Osimhen will actually be a good buy for Chelsea but considering the pattern of football in England, it will actually take him some time to blend well and cope well enough.