I can see why somebody might view that as a counter argument intuitively, but as somebody who cares about the problem in a real, practical sense, it's immediately obvious to me that the point isn't to criticise the city's vacancy rate in a void, but to compare it to the potential waste. In a city where prices are disgustingly high and homelessness is appallingly common, the vacancy rate becomes much more sensitive to pragmatic criticism. Simply pointing out that other cities have a higher rate doesn't affect the criticism. Perhaps those other cities wouldn't benefit as much from lowering the vacancy rate. Perhaps those other cities would benefit a comparable amount, and we should hold them to the same criticism rather than declaring the criticism invalid.