Werner had a bad season last season and he has not lived up to expectations. Chelsea made a decision to replace him with Lukaku. If you look at the team that Chelsea have there is no room for 2 strikers and one of them will be benched. I cannot see them benching Lukaku when they bought him for as much as they did. Werner is out of favor in Chelsea and I expect him to look for a transfer out of there next season.
Not bad at all because he has a Champion League that is a dream of many legendary players. Totti, Baggio, Ronaldo de Lima, Ballack did not win Champions League. Werner got it so he did have a successful season.
Just failure in his personal performance.
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.
Tuchel seems to like Werner and I agree that Werner is useful if Tuchel use Timo to distance opponent defenders. He is very fast and can bring troubles to opponent defenders. Lukaku will take advantage of open space and score goals.
If Tuchel does not use Werner as a striker, I think he will satisfy what Tuchel wants from him, and will be important part of the team.