Bayern Munich did not make the wrong move by releasing Lewandowski from their squad, because apart from Lewandowski having been at Bayern Munich for a very long time, in the end the team also needed younger players to be included in the Bayern Munich squad. And besides, Bayern Munich can still dominate the Bundesliga, although it will be a little difficult for other leagues such as the Champions League.
It is not bad at all. They did not want to break their salary ceiling as well as strategy for old players. Decision was made le Lewandowski go and they have Mane as a replacememt that is good on paper. Mane is younger than Lewandowski and even if he lose this season, I think he can have a better contribution in next season. In additon, Bayern will have more time in next summer transfer to find another striker for their team.
Bayern are very disciplined with their management for transfer and finance that helps them to be a greatest club in Bundesliga and one of most successful clubs in Europe and Champions League.