I don't think you can read too much into it. Like you already stated, it's all about match ups in the tourney. Many of these games come down to the last shot or two. For example, who is really the better team, Wisconsin or Florida after last night? That game was so close and could have went either way.
Or look at the Michigan- Okie St game in round one. Which team is better? Michigan wins by one point after shooting 70+ % from 3 in the 2nd half of that game. Does that make them the better team? If they play 10 times, it might go 5-5, who knows?
It's too hard to determine in one game. You need to go by using all the data points over the entire season, and in that case, the Big 12 was very good, one of the top two conferences this year, and definitely better than the B1G.
I had B1G friends of mine telling me that the B1G was just as good as the Big 12 this year since they both put 3 teams in the Sweet Sixteen. Really? So putting 30% of your teams in the Sweet Sixteen is as good as putting 21% of your teams in?
There's a lot of debate to be had, that's what makes it fun, but you really need look at the entire season that each conference had. SEC had a few really good teams, and then nothing else. Big 12 was good top to bottom.