Aaron explains the fabric of Philly as being a collection of small towns without a real city identity. Steve W, in one of the comments, further explains the relationship between the University of Pennsylvania and West Philadelphia. One could see this in stark contrast to the relationship Columbia and NYU have with their surrounding neighborhoods.
Alan Ehrenhalt devotes one of the chapters of The Great Inversion to Philadelphia, and explains another unique character of Philadelphia: its concentration of row house homeowners. Moreso than any other comparable city, Philadelphia is a city of families who own their own row houses. Alan describes how in our new reality of demographic inversion, this hinders large scale developers which are more successful in other cities. In Philly, a single holdout is more likely to impede the development of a large scale modern apartment building in an improving neighborhood.
Taken together these yield some interesting conclusions about Philadelphia. The established low-rise community-oriented character of Philadelphia act as a moderating force for the city. The community will serve as a stabilizing force during decades of decay, but will also prevent it from feeling the current wave of gentrification (for better or for worse.)
While I wouldn't argue that Philadelphia was a safer place to be in the 70s than New York, Boston, or DC, I'd say its trough could be more compared to Detroit. In terms of the positive change, Philadelphia is still an anomaly on the east coast. It remains the cheap option to those who want the large city urban east coast experience. Even the most expensive neighborhoods in center city are extremely affordable when you're comparing them to other large cities in the Bos-Wash corridor. Of course this also means the poorer neighborhoods of Philly are more destitute than comparable neighborhoods in other cities, so while displacement hasn't happened to the degree it has in other cities, there isn't as much in city opportunity available to people from these marginal places.
