Sadio Mane couldn't give quite the expected performance when he played as a centre-forward. And it is totally normal as well. Because he isn't naturally a centre-forward. Besides he has much more different characteristics than Lewandowski. The thing Bayern Munich need now is to sign a complete forward like Lewandowski. This can help them seriously about pulling themselves together.
Choupo-Moting tried to do some good things there but it wasn't enough unfortunately. Bayern Munich need a more reliable striker immediately. If Mane play as a left winger as well then their attacking line would be really strong.
I totally agree with you, I think Bayern's management is also very aware of this, they really need a single striker like Lewandowski and in fact Kane is a suitable candidate, but does Bayern not have other candidates who might have the potential to become the next Lewandowski, there must be a lot another, less exposed striker who could be a substitute for Lewandowski.
Sadio Mane has pretty much damaged his career by joining Bayern Munich. Because it was at Liverpool that the game performed incredibly well and his career progressed tremendously. But his performance at Bayern Munich has not been noticeable so far.