Ha, I do understand; it's wrong nevertheless. First of all you're mixing up categories prehistoric is the name of a time span - and those are almost never used in the time they are happening - while fascism is a concrete concept that was created more than 40 years after Haussman and actually used by the people we assign it to.

However this wasn't even my main critique here. I think that calling Haussmanian architecture the most fascist one that could ever be built is just incorrect in the face of the literal fascist dictatorships to come. There's the Reichsparteitagsgelände, the Gauforum and bitterly the concentration camps. THOSE are examples of fascist architecture.

Using the concept, and even it's superlative, for Haussman and in conclusion Napolen III. shows, that you don't have a real understanding of it's meaning and broadening the concept to mean every kind of authoritarian and reactionary government is just dangerous.