Philly has a more significant transit system than both Dallas and Atlanta. Philly's is more equivalent to Boston than the former.
As for Philadelphia having room for growth. I absolutely believe that there is room to absorb. especially when you consider how much Philly hollowed out, especially North Philly. To give you an idea, Philly's population was 2 Million in 1960 (now 1.6 million), and that was prior to the development of Northeast Philly, which currently has over 500,000 residences. Yes, family size is much smaller now, however, average family size only changed by about a half a person, not half. (3.67 to 3.14)(
https://www.statista.com/statistics/...ily-in-the-us/). So by my calculation, the rest of philadelphia (excluding the northeast) could hold 1.7 million people (2million * 3.14/3.67), when you include the Northeast, you are looking at 2.2 million residences, so I would imagine you could increase the population of philadelphia by 600,000. Obviously this is a rough estimate, but regardless, I don't think people realize just how big philadelphia is, how much it emptied out (sadly), and how many residences the city can still accommodate. I know Dallas and Atlanta can density, but for Philly, it would be more infill and you would not really need to increase infrastructure.
With that said, good things don't happen to philly, even tho it would be good for it.