I don't view Colts-Texans as a rivalry. Yet. The Texans were just not good in the first years and couldn't really compete with anyone, much less the Colts. We started getting decent around 2007 and started playing close games with Indy in 2008. In 2011 when we got really good the Colts were terrible without Manning, and that second meeting was Yates and no Andre after we clinched. Maybe this year is the start of a true rivalry, it's kinda crazy that the schedule is the way it is, having it build up to be a really good matchup late in the year.
The only rivalry we've really had is with the Titans, because they used to be the Oilers and we hate Bud Adams and everyone hates the Titans anyway.
I would say the Texans were NOT horrible per say. They just had no answer for Peyton Manning. That's why Mario Williams was drafted in 2006 vs Reggie Bush by then GM Charley Casserly. Hiring HC Gary Kubiak was also a smart move that turned the fate of the Texans for good IMO in addition to acquiring RB Arian Foster as well.
Also TBH, DC Wade Phillips fell in your lap & he was a God send after being fired from Dallas in 2010 because your pass rush, secondary, and DB coverage was simply awful before Wade showed up in Houston.