Regarding Boeheim's track record in the NCAA Tournament, I actually don't think he's underachieved all that much recently (this season notwithstanding). In 2012 they lost in the elite eight, to Ohio State, without perhaps their most important player - I have a hard time calling that a colossal failure. Obviously in 2013 they didn't underachieve. In 2010 they lost in the sweet sixteen to the eventual runner up without a key player, and in 2011 they simply weren't all that good. You want underachieving in the tournament, look at Coach K. I've never seen a guy lose to a fifteen and fourteen seed within a three year span and take less grief for it.
I also think there are a lot of misconceptions regarding the zone defense. He's been incredibly successful with it, and I'm slightly baffled that people still question it. Syracuse's collapse this season had absolutely nothing to do with the zone and everything to do with their players suddenly forgetting how to play basketball. Syracuse's defense last year was as dominant a unit as there was in the country. Generally speaking, when Syracuse loses in the tournament, it isn't because of the zone.
In the last five years, Boeheim is 149-32 with three sweet sixteens, two elite eights, and one final four. He's won two conference titles in that span and turned in a more than respectable 11-5 tournament record.
Tom Izzo, on the other hand, is 135-50 with four sweet sixteens, two elite eights, and one final four. He has tied for two conference titles and also gone 11-5 in the tournament.
Shorten the sample to three years, and the results swing in Boeheim's favor - Jim is 92-19 over that time frame with a conference title, two elite eights, a final four, and an 8-3 tournament record. Izzo is 85-26 with a split conference title, three sweet sixteens, one elite eight, zero final fours, and a 7-3 tournament record.
They are very even, but one guy is viewed in a better light than the other. To me, it is a coin toss.