Taking the second point first - SJP doesn't have a connection to the down cycle in the Valley. If I'm not mistaken, the only Lehigh Valley kid who went to play at SJP was Davion Kidd-Jackson. I think I went through this in another thread, but I think you have coaching disasters at varying degrees at a lot of the schools that should be the best schools in D11 (Easton and Liberty mainly, but Becahi also less with more than any program in eastern Pennsylvania). Parkland is in a little bit of a down cycle (relatively and after being really good from 2011-2016), but the ecosystem's teams that should have naturally filled that can't get out of their own way. And going back, I don't think it's an accident that Liberty's run of being very good (in addition to Moncman) coincided with Bethlehem Catholic bottoming out after Stem left; or Parkland's real rise coinciding with Morgans leaving at Allentown Central Catholic in '98 and that program bottoming out before Fairclough (and him eventually going to Parkland). Right now, the Lehigh Valley looks like the Big Ten if Ohio State (Parkland) took a step back, Wisconsin (Easton) and Michigan (Liberty) both had total clowns as coaches and were missing bowl games, and Penn State (Becahi) was landing monster recruiting classes, but losing 3 games every year anyway and missing the conference title game. It's great for Northwestern (Nazareth) or Iowa (Freedom) can win the league, but they're not going to the College Football Playoff ever because they just don't have the built in advantages to be that kind of team.
The District 1/Philly in general effect may be greater than you think. Different sport, but if you look at the after effects of the mid-1990s to early-2000s transfer bonanza in the Lehigh Valley wrestling scene, with Easton, Nazareth, and Northampton loading up on guys from other schools to make these super teams, it set Valley wrestling back a decade. There was a real dip in how competitive we were at the state level, partly because all the programs that used to produce a state champ contender every so often completely dried up. It hurt feeder programs, it hurt the competitiveness of the season (which hurt fan involvement), and it created a coaching brain drain, because who wants to go take the Whitehall or Freedom job just to get your head kicked in when you can leave the area and build a winner. District 11 got significantly worse in the process, and it took a solid 10 years to build it back up. The analogy isn't perfect and I don't know the D1/Philly football ecosystem as well as I know the Lehigh Valley wrestling one, but I see a lot of parallels as an outsider.