Well, unless you think that Kubiak caused: the Chris Brown fumbles, the Steve Slaton fumbles, the Ryan Moats fumble and the odd overturn of the call at Indy, the Kris Brown missed FGs, the Bironas made 53 yd field goal, the Schaub interception at Arizona, the Schaub injury vs. Jacksonville, the Colts laying down versue NYJets in week #16, the Bengals laying down vs. Jets in week #17...
Unless he's responsible for every single one of those things, then clearly Kubiak can make the Texans a playoff team. Because, if any of those things happen differently, the Texans are in the playoffs.
The real question is whether he has what it takes to elevate the team's play enough to overcome a lot of misfortune. Last season, he couldn't quite get it done. I do believe he can, though. However, next season we could breeze to an 11 win season without him being tested in that way. So, it's a question that may not get answered for 2-3 years. Next season, I'm hopeful we get a few more bounces, we're even more talented and experienced, and we stay relatively healthy. If all that happens, he could coach this team worse than he did last season and we'll still be in the playoffs.