The process that resulted in the hiring of Wade Phillips was disgusting.
Following the hiring sequence that has often been set out by the Texans, which can be expressed in the question: "Are there any coaches that used to work for the Denver Broncos that are available?" The Texans have a new scheme, a new vision, and a clean slate...on defense. This is still a team that has no discernible head coach/general manager hierarchy, still has no clear structure for accountability, and every sign points to them not having learned any lesson from the past few years.
However, just because the front office remains committed to poor decision making as a whole doesn't mean that hiring Phillips can't be a net positive for the Texans. A combination of factors, working with simple regression to the mean, will force the Texans defense to be better. Just how good they can be will be decided by what moves they make to bolster their talent in the offseason, but there are plenty of reasons to think that even with the talent on-hand, the Texans can be a better defense than they were last year.
1) Wade Phillips' defenses typically are very solid.
While the Texans were a bad defense all-around last year, they were especially bad against the pass. Kareem Jackson was given a baptism by fire as a starting cornerback, Bernard Pollard is purely a run-stopper, and Eugene Wilson vied with Troy Nolan to see who could be the worst starting safety in the NFL. Completed Hail Marys, last second comebacks, and tipped passes that landed in the hands of opponents were among the comedy of errors that this defense had allowed to happen. By Football Outsiders DVOA ratings, the Texans were roughly 37% worse than the average NFL defense against the pass.
Wade Phillips has had a long and prestigious career as a defensive coordinator, but the consistency is what is most alarming when you look at his statistical record.. Up until last season, Phillips' Cowboys had ranked as an average or above unit against both the run and the pass all three years that he'd coached them. In fact, other than his 1994 season in Denver, his 2003 season in Atlanta, and last year in Dallas, Phillips has put together an average or above-average defense by Football Outsiders' DVOA in every season he's coached that we have advanced statistics for. That's 14 of 17 seasons. Including every season that he started anew with a team. In 13 of those 17, the teams that he's coached have been average or better at pass defense specifically, meaning he should be able to improve the biggest weakness the Texans have.
2) The injury situation will trend toward the mean.
One of the reasons Football Outsiders projection system pegged the Texans defense to regress in 2010 was that the front seven was so healthy in 2009. 16 games of Mario Williams, Antonio Smith, Amobi Okoye, DeMeco Ryans, and Brian Cushing were a big reason the defense was as good as it was in 2009. Fast forward to 2010, Ryans and second-year sophomore Connor Barwin both were lost for the season early, Cushing had his four game suspension, and Williams eventually missed the first games of his career due to a sports hernia.
Am I saying the Texans will all be back in supreme health next year? No. But it's likely that they won't lose quite as many games to injury or suspension next year. Especially not to their most important defenders: Ryans, Cushing, and Williams. This should point the defense up at least a little bit.
3) Youth will be served.
I know it seems like we say this every year, but the Texans had one of the youngest defenses in the NFL last year. Once they discard the sure riff-raff like Xavier Adibi, Brice McCain, and such, the talent that is on this defense should trend upwards. It's unlikely that Jackson will be quite as bad as he was last year with a year under his belt, as rookie cornerbacks as a whole are notoriously slow to adjust to the NFL. Barwin, Glover Quin, Daryl Sharpton, and Sherrick McManis, among others, will all benefit from a(nother) full off-season under the team's guidance, particularly under a coordinator that actually knows what he's doing.
4) Unbalanced defenses are easier to fixed than balanced ones.
By this I mean: we all know that the Texans have the stars on defense. Williams is one of the purest pass rushers in the NFL, Cushing was a monster in 2009, Smith and Ryans (should his injury comeback go according to plan), while not stars, have consistently been very good players for the Texans.
The problem that the Texans had last season, a problem that they've had for many (all?) of their seasons, was that they essentially started non-factors at four spots on defense: nose tackle, outside linebacker, #2 cornerback, and free safety. You could quibble with possibly adding Pollard to that, but I think he just had a bad year. Either way, it's much easier to fix personnel problems when you're trying to hit average than it is when you're trying to find a star. It would have been very easy for the Texans to go after a solid safety in free agency last year. While the expiration of the CBA restricted player movement, solid cornerbacks like Antonio Cromartie and Josh Wilson traded hands freely as the Texans sat on their hands and let Jackson start.
It's just not that hard to upgrade to solid at every position on the field. As long as the Texans realize that and chase it, it won't be too much to ask for the defense to take a step forward next year. With Phillips calling the shots and Kubiak apparently willing to give him whatever he needs, it would not at all be surprising if Phillips turned over most or all of the problem areas on the roster this offseason.
5) Phillips isn't married to these players.
One of the biggest problems the Texans faced last year on defense was their own complacency. When faced with enough empirical evidence to decide that Jackson wasn't ready to play every day, the Texans stuck their heads in the sand and kept repeating buzz words like "battling," "needs to do better," and "he's the best we've got."
The same can be said about Zac Diles and Wilson. These three were just tremendously bad last season, and the Texans defense suffered for it. Instead of fixing the schemes that hurt them, or finding players who would fit those schemes, Frank Bush hid behind his "really good defense after the first three weeks last year" facade and kept throwing out the same guys who weren't competing. Shockingly, they continued to fail him.
Phillips doesn't have the same problem. He didn't draft anyone here (yet), and he has no reason to favor anybody based on old plans that didn't work. If he sees a player that isn't ready to play, he'll go out and find someone who can. If we're in a situation like last year, where a Jackson or Diles is still starting and struggling four weeks into the season, Phillips can freely bench him and let someone else start. While the Texans weren't going to turn their defense from abysmal to good with these moves, it was clear that the defense at least played less terrible when Jackson was replaced by Allen and Diles was replaced by Sharpton. Phillips will have no incentive to wait it out on players who aren't performing, so it's likely that those who don't will have less snaps wasted on them. Which is always a good thing.