I think, yes, it was arguably the best ISU roster of all time. The most interesting comparison might be with Johnny Major's 1971-72 Liberty bowl team that, similarly, went 5-6-1 (NU, OU, and CU finished 1, 2, and 3 in the polls that year) and had a number of players that went pro.
Several of the 2011-12 players mentioned are hanging around on rosters more than one year having been undrafted free agents. Historically, ISU players are undervalued on draft day due to the less than stellar achievements of the team, and the fact that we live in fly-over country. As UFAs, though, they do have the advantage of standing out versus their perceived peers for that reason.
So why the apparent underachievement of the 20011-12 squad of finishing 6-7? The Steele Jantz injury at UConn was a factor. Remember, too, that KO played the entire season, as much as he managed to play, on a sprained ankle. And Bykowski (gotta mention our MN boy ...) was never on the field with KO at the same time. He played often, but only as KO's backup.
But, in my mind, the tale of why the 2011-12 squad was 6-7 and not, say 9-4, is told by the final 2011-12 Jeff Sagarin ratings:
http://www.usatoday.com/sports/ncaaf/sagarin/2011/team/
ISU finished #43 overall. Don't have a link, but I recall they would have started the season ranked in the 80s. By this measure, the teams achievement versus expectation was truly historic. Compare that to Iowa, who finished #45 and probably started in the 30s. (I'm sure it will not be lost on Lakesbison that NDSU finished #37 that year, about where I'm guessing they would have started out.)
But I think the biggest factor for ISU in 2011-12 is that, according to Jeff Sagarin, they played the #2 overall Strength of Schedule (Iowa was #39, and NDSU #136). According to Phil Steele's retrospective rankings, ISU did in fact play the #1 SoS in the nation. Anytime you play a top 10 SoS, your team is going to be physically beaten up at the end of the year, and you have little chance of making it to a bowl. It also shows how absolutely miraculous the OSU win was that year, late in the season, with a freshman QB, and on ESPN in front of the entire CFB world. <-Cy->