I can't say Sadio Mane is a flop now, but he still hasn't found the game he's used to playing like at Liverpool. Bayern Munich still haven't found the chemistry between their new signings. I think he still needs time for that, to get the best out of him. Even though it takes time, I'm sure Mane can show something that is his strength. The league has only started a few weeks, it's not as expected but we have to be a little patient to see Mane.
Now is not the time to conclude that, because all the new players have not played so long this season in their respective teams. And also each new player will need a different time to adjust to the old players in the team they occupy. For example like Mane where he hasn't fully adapted to the Bayern Munich team this season as you said and I think that's true. So it would not be complete if we had to conclude now for every achievement of all new players including Mane.