If Stevens had stayed at Butler, the level of talent he was going to coach wasn't going to be any huge step up from what he already had, especially in 2010. I think it's a huge mistake to just assume, because of what happened in 10 and 11, that it was going to continue to happen.
It's the easiest thing in the world to look at a coach at a smaller school and say "Wow, if he had X's talent, how good would his teams be?" In Stevens' case, had he stayed at Butler, there's no reason to think that there would be a huge uptick in recruiting (when you get Gordon Hayward, regardless of where he was rated coming out of HS, how much better do you think you're going to get?), and what he would have done even if there was will remain a mystery.
I assume he would have had very good teams, but assuming he'd have won a title in the last 4 years (because that's all he's been out of the college game) is a step waaaaaaaaay too far for me. Too many excellent coaches at bigger schools, with easier access to elite talent, have made a big initial impression and then struggled for years to win a title for me to think Stevens is so great that he could have done it in the last 4 years. Maybe he could have turned Butler into the Duke of the Midwest, and gotten to the point where he could compete for nationally known recruits, but there are factors working against that, and I think it would have been a fairly long process, kind of how Gonzaga had to remain a factor for well over a decade before they could start getting really high level players (and even then, mainly as transfers).