This is a matchup issue that we will not face many times this year. The middle zones were all about keeping linebacker and nickel/dime players facing the line of scrimmage, the Texans run so many zone runs using them as blockers that just manning up in pass coverage can mean giving up big runs. Add to that, the receivers for the Texans can block too, and it becomes easier to understand.
Maybe we can give a little credit to the Texans here. They have a QB whose strengths lie in throwing up the seams, and they are good at getting him looks in those areas. You can look long and hard through the league and you won't find many linebackers who can key on the run and still play good pass coverage. It is the Texans strong running game that forces linebackers to make tough decisions, so much respect to them.
As far as Jimmy Graham goes, if he kills us it won't be for the same reasons as the Texans. Brees has mastered the art of playing above the rim with Graham, they aren't freeing Graham up with zone block running looks, and in fact Graham is only servicable as a blocker. Like Wilson, Brees uses the margins of the field better and isn't often throwing to linebacker zones. I will be surprised vs the Saints if we are in many 3 or even 2 LB sets. In fact, I would not at all be surprised to see Sherman, Kam, or Browner iso on Graham and Thurmond cover their normal assignment.
I am more worried about Sproles.