You have forgotten the guidelines for cultural victories, and those are, that at least 1 city can be bombed to legendary without problems. Ok, that's not Hamburg specific, but it could hit Hamburg, because the city actually works quite a number of Artist-Specailists and has quite a lot Culture-producing buildings actually like various tons of Theaters i. e.
Thinking that Hamburg is the GP-Farm of Germany is supported by
this list of favourite persons that either came from Hamburg or lived there for a longer time.
See above, and I named Hamburg because it's the 2nd biggest city of Germany and didn't know which to choose as third. Hamburg probably is the GP-Farm and yes, the argument with the harbour was stupid.
You don't count the Oktoberfest, which is a great fiest of german beer-culture, but you count the that TV offers? Even if I followed your arguments, there are more TV-Studios in Hamburg and Munich than in Mainz or Nuremberg, and regarding german bear.
Also, Commerce = Culture via the Slider if you didn't know, and Hamburg + Berlin afaik have a Jewish Synagoge, an Islamic Moshee, and a Christian Cathedral, so if talking about close, those cities actually could produce enough Culture to get to Legendary really fast.
You also misunderstood my argument about Hitler, completely, which was, that he constructed quite a lot of culture giving buildings there, because he wanted to make it the capital of the world, but yes, many didn't make it and most got razed by Russians and Americans. Still, what's said above counts.