To quote the bastard Andrew Jackson: "John Marshall has made his decision, ; now let him enforce it."

Lawsuits brought on by individuals are only good to address smaller issues. Slightly better is the lawsuits brought on by a federal agency, but even they have their limits (see the show "We own this city"), because they have some level of enforcement and supervision, they still don't technically have direct power to hire and fire, and the problem with PPD is inaction, not criminality (in general).

There are certain thing that must change only through elections, and this is probably one of them. Not just the mayoral position, but the council positions too, to have the collective representatives be politically aligned against the PPD's bullshit. That's going to be difficult, because there are certain parts of NE Philly and South Philly that are going to scream "Support your law enforcement officers!" even as they get their teeth knocked out by cops, and those words start sounding funny without teeth.

TLDR: not a legal issue, it is a political issue, and it is hard to change.