Keith is usually good on big picture issues like this.
You're absolutely right on the Lehigh Valley feeling walloped at 6A by the "Philly freight train." After only missing the eastern final twice from 1996-2008 (with state finalists in 2002, 2005, 2006, 2007, and 2008), only 2015 Parkland has advanced past state quarterfinals. And while in the last three years, we haven't had that level of a team, I don't think the quality has been down for that entire 10 year stretch. 2009 Easton, 2011 Nazareth, 2013 Parkland, and 2014 Parkland were all legitimate finals contenders stopped by loaded PCL teams.
It's also not just football, and it's not just the PCL where things have gone sour. In wrestling, the Lehigh Valley broke things in the early 2000s. Easton, Northampton, and Nazareth definitely were the beneficiaries of big transfers to supplement already national caliber rosters. But then, when Alex Meade got blocked from going to Easton in 2008, you got real enforcement of public-to-public transfers. That didn't stop kids from changing schools, but has had the effect of making the only feasible transfer to Bethlehem Catholic because it was much harder to prove intent going public to private and there were no address shenanigans or moving needed. It's our fault for starting it, but Becahi (and now Notre Dame) have taken transfers to their logical endpoint in a way Easton, Northampton, and Nazareth couldn't.