I'd argue after having lived in China and Hong Kong for numerous years that very few major western metropolises have proper authentic Chinese (and Chinese food is vast there's a huge amount of differences between regions).

For example, try getting proper cantonese dim sum in Paris or Barcelona. I only know 2 places in Paris that are halfway decent after having searched quite a bit. Or try searching for good Zhejiang food (the Hangzhou or ningbo style) in Europe.

And Chinese food in most of the US is bastardized to make it much sweeter and oily to conform to the taste there making it absolutely terrible and far from authentic.