For Werner, he was improved in last phase of past season but it is not a guarantee for his performance in this season. Moreover he wants to get more opportunities to play and want to be in Germany squad in World Cup. Returning to Leipzig is what he wants and Chelsea decided to let him go.
I think both cases are good from Chelsea side and good for future of two players too.
I think Werner is good, lucky Leipzig got him. Indeed, some good players if they don't fit the player's criteria then they won't be needed. The decision to leave was right, he would have got more playing hours if he was able to perform well in Leipzig.
But in history when he was at leipzig from 2016 to 2020 he was always the top choice, he almost played more than 30 times in the domestic league. Although indeed he did not score too many goals. as an assailant. He's far behind haaland or Nunez.