Bayern Munich's performance has been erratic since the sacking of Julian Nagelsmann. But we can't blame Thomas Tuchel for that.
Tuchel did not have much time in Bayern Munich before some important matches in Champions League and Bundesliga. First he brought hope to Bayern by directly beating Dortmund. Later Bayern got unstable performances and they luckily won Bundesliga at very last minutes of the season with a genius moment from Musiala and very poor performance from Dortmund.
Bayern Munich management sacked Julian Nagelsmann at a strange time. Such a decision was taken by the management before the crucial match against Manchester City.
Tuchel has his record to help Chelsea winning Champions League as an alternative coach since winter transfer. I guess Bayern Munich tried to bet on Tuchel and they really wanted to win Champions League. It is pressure from their not too good finance after Covid-19.
However, players need time to adapt to a new coach's formation or match strategy. Tuchel will also find Munich's weaknesses now. And Tuchel needs to be given enough time and opportunities for that. It is expected that Munich's performance will be more organized in the next season.
If Mane plays better and if Bayern find a good striker to replace Lewandowski, Bayern Munich will become a stronger club in a new season and they will dominate Bundesliga again. Their chance in Champions League will not be small because in a new season, many big clubs will be in transition phases like Real Madrid.