I don't have a hard time believing that Casserly convinced Kubiak that Mario should be the guy. I don't have a hard time imagining that Casserly evaluates talent pretty well. He made his way into the NFL via the scout ranks, I believe.
Look at the players he drafted or acquired for the Texans. There have been some busts along the way, but there has been ample indication at this point that Capers and staff had as much or more to do with those busts than anything. In no particular order:
Gaffney - Bust? Certainly not a #1 WR caliber, and probably not worth a second round pick, but he's a contributor, and probably a legit #2 WR on many teams. He certainly would be a #3 WR for most teams.
Seth Wand - Bust? Well, he didn't succeed in the NFL, so yeah. BUT - he was given a shot as a rookie, and he fared better as well as Pitts had at the LT spot. Then he never saw the light of day again when that genius Pendry benched him. He showed more than Spencer has shown to this point. He could have developed, but we'll never know.
Babin - Bust? Well, he was playing out of position, then he was injured, then he played part-time for Kubiak and got after the QB pretty well as a situational pass rusher. Not a bust, IMO, but he would never be worth the 3 picks given up to acquire him, even if he made the Pro Bowl.
Travis Johnson - Bust? Well, he was when Capers coached him. He seemed to have an attitude problem, and definitely didn't live up to his draft position under Capers. But he's showing us now what kind of talent he has. Cass saw the talent, but Capers didn't get from TJ what Kubiak and Co. is getting from TJ.
Marlon McCree - Acquired in mid-season and took over the job from Matt Stevens. He performed well, and may actually still be the best FS this team has had. In his second year with the club, he seldom saw the field because Capers moved Coleman to FS. McCree left and became a quality player elsewhere.
Steve Foley - Pro Bowl in SD before he went bonehead and died to the cops.
Weary - Didn't do much of anything until Kubiak got here, and now he's a decent player.
Clark Haggans (sp?) - Capers told Cass that Haggans wouldn't be a good fit here in Houston, so Pittsburgh got him to be a starter in the 3-4 and he now has a SB ring. Cass brought him in for a tryout, IIRC, and Capers didn't want him.
Greg White - couldn't make this team when Capers coached here.
I'm sure there are more; I am just riffing off the top of my head. Also worth mentioning are the players that came here from other teams and got worse, along with the players we drafted that declined over time. Very few players that were coached by that Capers staff ever got better. You really think Anthony Maddox, Thomas Johnson, or Earl Cochran would have done anything here under Capers? Those are Rick Smith acquisitions that we all laud for their value in critical situations.
Casserly killed this team by spending draft picks inappropriately, giving too much money to average players, and mucking up deals involving draft picks. On the talent evaluation front, I don't put him any better or worse than your average GM throughout the league. The deals were brutal, though, and that part of his job was ultra-important to an expansion franchise. You can't afford to waste away three draft picks on a player like Babin. You can't afford to give away draft picks for Buchanon on two games worth of film. You can't pay Todd Wade and Morlon Greenwood money like Orlando Pace and Ray Lewis.
As I said elsewhere, Casserly has a seat at the head of the table for who takes the blame here in Houston, but it wasn't necessarily his talent evaluation that killed the team. JMO, of course.