Fine, on some things they are close but Nichols has thrown for more tds per game, thrown less picks per game, thrown for more yards per game and has won more games over the past three seasons. Nichols has also gone to the playoffs all three years and didn't get replaced by his back up in one of those seasons. At this point, Nichols is a better QB and is trending in a better direction.
For sure it is never one thing but in football the lack of a QB kills you, just like the lack of a point guard kills you in basketball.