It's population declined from 2.4 million in 1914[1] to 1.5 million in the 1980s[2]. The only reason why it's currently considered even close to a world-class city is that after the fall of the Berlin wall it was the natural financial hub for oligarchic capital.
I think we can all agree not many great and global cities have tons of free housing emptied by a prolonged period of decline. And that we can't really evaluate if the city is solving the economic problem well or badly, as right now it's simply less acute for historical reasons that have nothing to do with it's housing policy.
[1] https://ww1.habsburger.net/en/chapters/growing-city-vienna-e... [2] https://www.macrotrends.net/global-metrics/cities/20107/vien...