It is not expected that he will score 28 goals in 34 matches in the 2020-21 season, having scored only 6 goals in 35 matches in the 2019-20 season. He has abilities. We've seen gameplay from him in the past. He can't adapt himself to this team. If we could adapt, the performance would not have deteriorated. Moreover, he needs more experience.
There is nothing wrong with what you say, he really needs time and effort to adapt well to his team which will give him experience. Tuchel may be able to give him plenty of chance to get more playing time in this busy season and Werner should make the most of them. There's no way Chelsea would be interested in him just to sit on the bench all season. If this season Werner fails to play well, then next season he will not be in the Tuchel project again in my opinion.