Don't let the fact that the defense played their best game of the year impact the eye test of a mediocre 22 point effort by Orton in a home game. There was a tremendous drop between Romo and Orton in Week 17 as evidenced by Orton's 1:1 TD to INT ratio and Romo's over 3:1 in the 2013 season, which is pretty damn significant. 28 quarterbacks last season attempted at least 300 passes last season. The group with over a 3:1 TD:INT ratio were Romo, Alex Smith, Nick Foles, Peyton Manning, and Drew Brees. That's four passers who made the playoffs, and a fifth who had his team a game out with a broken back going into Week 17 with the worst defense in the NFL. The 5 starters with a 1:1 or below ratio were Flacco, Henne, Schaub, Eli, and Geno Smith, and we know how those offenses performed.
As for the drop-off to Kitna I think you need to go apples-to-apples on that one and compare the time where Wade as the head coach. That was the team Romo QB'd under before that team was reborn with some discipline, and they went 0-2 with the Wade and Kitna starting combo with 2 TDs to 6 INTs and getting outscored 24 to 80.