The first mention I could find of “gritty Philadelphia”  was a June 16, 1880 article in the Boston (Daily) Globe about a walking contest known as the Sawdust Pounders.

Some more examples of gritty Philadelphia people.

A 1976 profile of Bill Green syndicated by UPI appears to be the first use of “gritty Philadelphia politics”.

By 1986, a usage familiar today—that of the gritty Philadelphia neighborhood—appears in a blurb about the novel South Street.

In 1989, NBC used the phrase to describe the lead character in a new legal drama.

The uses above seem clearly positive, evoking the Angela Duckworth sense of the word. But grit is not always a good thing. “Gritty Philadelphia” sometimes just means dirty.