You can throw stats out the window. He spent his entire career in the most QB friendly offense, in the most pass happy era in NFL history.
What you need to look at is big situations.
2001 NFC Title game - Potential game winning drive to put the favored Eagles into the Super Bowl, and he throws an interception to end the game.
2002 NFC Title game - Potential game winning drive to put the HEAVILY favored Eagles into the Super Bowl, and he throws a pick-six to Ronde Barber to end the game.
2003 NFC Title game - Three interceptions and a horrid performance against the Carolina Panthers.
2004 NFC Title game - Beat the Vick lead Falcons. lol
2004 Super Bowl - Three interceptions, including 1 in the red zone. Down 10 points with 8 minutes remaining, Eagles have the ball with a chance to get back into the game. McNabb is dry heaving in the huddle, and is "too tired" to call plays. Freddie Mitchell had to call plays. Story confirmed by multiple offensive players inlcuding Olineman on the team.
That alone should prevent him from getting in. Hall of Fame should be reserved for the greats that RISE to the occassion.
I'll give you he had a great performance against the Cardinals in the 2008 NFC Title game.
But I've long stated that those Eagles were near dominant for so many years because of Jim Johnson's dominant defenses.
McNabb is a better than average QB who benefitted from that defense, a relative weak era in NFC football, and who too often crumbled when the pressure was highest.