Munich is neither bad nor small but still I can imagine
  that finding friends there is hard: in Munich you find
  those networks and circles which exist for decades and over
  generations. The people are nice but the fluctuation is too
  small

Compared to the US, you find decades old networks and circles nearly in every part/city of Europe (at least in Germany). This is just a result of a quite immobile society until recently. In Munich, fluctuation among young professionals (20-40) is actually pretty high, or at least higher as you describe: Munich is one of Germany's economic powerhouses with lots of German graduates and professionals from the rest of Europe moving to.

  the city is not dynamic, night-life is quite limited, you
  would need 10 years to get into the society and still some
  parts would not welcome you.

I don't really know what you want to imply here: how do you define dynamic? And what should it mean in this context? Munich might not be as dynamic as London/NYC/SF/Berlin/whatever, but calling it not dynamic doesn't do it justice.

The rest of your statement is also very prejudiced: it does not take you 10 years to get into the society, and that some parts of every society are not open to foreigners is neither unique to Munich, nor to Germany or Europe.

Regarding Munich night-life: it is definitely not comparable to Berlin night-life, but still it is quite vibrant. There are two of Germany's biggest universities in Munich, and roughly >110k students in the city. In summer time the whole city is out drinking/eating in one of the millions of beer gardens where it is quite common to sit with total strangers at the same table.

  => change quickly to a real capital

Depending on your field, Munich sometimes is THE place to go/work in Germany: i.e. you won't find a lot of engineering positions in Berlin, but lots of in Munich (or generally speaking in southern Germany; but then Munich most probably is the most open/international city there).