It's an interesting post, but there are several different components that played a role in it. One, early in the season the NFL defenses weren't expecting much from the Texans, and with only one season of film to work with it took time to develop a scheme to slow the offense. Often in the NFL you'll see offensive numbers blow up the first few games for several NFL teams till the defenses adjust and bring it back towards the norm. Secondly, injuries played a key role in the conservativeness of the offense. After David returned from his shoulder injury late in the season, his arm was most assuredly not 100% and therefore was not as capable to make throws downfield against even mediocre DBs covering. Add that to the fact that the often injured defense had a hard time stopping anyone means less time on the field for the offense thus fewer chances to gain yards. The injuries would also lead the coaching staff to adjust and throw in safer plays to get DC comfortable. Thirdly, there is much to be said for the strength of schedule as the seasoned progressed. That coupled with the injuries would skew the offensive production some. The reasons go on and on from rookies hitting the 'wall' to even wear and tear on the team as a whole as it gets later into the season.
Dont get me wrong, I think the numbers you put forth are interesting, but in the NFL a running game is very valuable. It gives you the ability to control the ball longer and thus a greater chance to win the game. I'm sure even DC would tell you that he was thankful for a running game, and a good dependable dump off guy. Also, I believe that if DC's progress has been stunted its more a product of his own actions as opposed to having a dependable dump off option. I feel that you'll see much more progress from Carr in his 3rd year, as I assume many others do, and he'll surprise many people. Look for him to start making his other reads as opposed to only his primary read like he did much of last season. If you want a good example of a reliable dump off guy look at Green with the Packers, or Faulk a few years ago with the Rams. If anything it allows more chances to turn a negative play into positive yards. Good stuff nonetheless.
BTW Tried to make an equally long reply, but I feel I came up a bit short. Oh well maybe next time.