Had to look it all up to be sure... that my memory wasn't failing me...
Allen had a career 56.3% completion rate and an 83.something QBR. Those don't look like HoF numbers at a glance. He had a HoF career, but few QBs get so many years to fill out their stats.
Allen's completion % improved and trended upwards late in his career... without a string of later seasons of 60%+ his career accuracy would be downright brutal.
Clearly his running ability buoyed his... less than stellar passing skills. He parlayed his athleticism and ever-growing experience into a very long career that allowed his passing yardage and TDs to pile up. It takes nothing away from his illustrious career to say his longevity helped him pile up the stats.
All that said, it is unforgettable how Allen went off in his 40s, he sat a lot of critics down with his Grey Cup MVP followed by 5000 yards and CFL MOP the next season. He's the exception that proves some guys still can get it done well past the usual expiration date