I see what you're saying--but I don't think it really works that way.
I don't think people look at NYC and say "Hey if it weren't for NYC, Philadelphia would be the country's financial, cultural and diversity capital"...anymore than they would say Boston would. I don't think philly would necessarily, automatically just adopt that "gravitational pull" if NYC didn't exist tomorrow.
Philly is not a "mini NYC", the landscape, the people etc is just entirely different. I don't see Philly having the second largest population on the east coast along with being 100 miles from NYC as some sort of qualifier. I honestly couldn't tell you who would be next in line between Philly, Boston, Jersey City or Newark.