Pretty simple why the Pens aren't higher than the Islanders or Flyers.
We've played the Flyers I believe 11 times in the playoffs and we've won about half the time. I started following them when they were the Broad Street Bullies thru the Dave Brown, Rick Tocchet days. They were a nasty mean ass team pretty much every year and most Ranger fans hated their guts more than the Penguins than and to this day.
We've played the Islanders I believe 9 times in the playoffs and once again we've won about half the series but most if not all of them have come from 1990 and onward. I don't need to go thru the pain that Ranger fans like myself went thru early to mid 80's while the Isles were winning their Cups, they were stepping over our asses despite us giving them all that they could handle. To this day and it will never change most Ranger fans hate the Islanders more than the Penguins AINEC.
We've played the Devils I believe 6 times and once again we've split with them. But when they were good, we were as well just not as good as them during those Cup years of theirs. They had some very hateable players...Claude Lemieux, Kenny Danyko,Marty Brodeur. Not even close for peeps my age to hate a metropolitan rival more than the Pens.
We've played the Pens I believe 6 or so times and we've had a fair amount of success vs them in the playoffs especially the last 15-20 years. The only time I can truly recall the Pens breaking my heart was in the '91-92 season when Messier first came here. That year most Ranger fans like myself thought we were going to slay the dragon. Well Lemiux, Jagr, Barasso, Ron Francis had other designs. The Center ice goal by Ron Francis in Game 4 past Mike Richter still puts me in a sour mood just thinking about.
So no question Pens are 4th on that list and it's really not even close. And I'd bet if you ask any Ranger fan over 45, they'll give you similar rankings....Isles/Flyers followed by Devils and either Pens or Caps and maybe the Bruins. Whoever you pick for 4th is WAY behind the other 3.
Hope that enlightens you....cheers!