The defenses are a world apart.
Arizona has a bad one, and Philly's at that time was VERY good.
As for offense... McNabb had a decent O-Line back then (whereas Leihart's isn't good at all) and McNabb also had Duce Staley who was havibng good years. In fact, Staley had his best year in 1999 with 1,200 yards rushing.
http://en.wikipedia.org/wiki/Duce_Staley
(i.e. he had a decent running game vs. NO running game to take the pressures off of him)
So I disagree here... I think that McNabb had better support on offense as well... if ONLY because of the O-Line.
the ONLY area on O where Leinhart has an advantage is at the WR position... which is minimized when you get sacked as much as Leinhart does.