If you’re an American declinist type, most of that slippage will come in the “political power” category, where D.C. still ranks number one. If you’re an optimist, it might not be so bad, if D.C. manages to get its economic act together and raise its ranking in that category from 31st place to something more respectable.
One might argue that Washington’s popularity with the wealthy shouldn’t matter as much as livability and affordability for all classes, but I’d counter that a city with excellent quality of life, global political reach, world-class educational institutions, and economic girth offers more opportunities for everybody.
Anyhow, the whole thing is worth a read.