From 2006 - 2009 Bronco had a really great run. (It should be noted, though, that during those years he was to a large degree playing Crowton's recruits.)
But from 2010 on, I've seen his teams disappoint year after year (2011 somewhat excepted, albeit against probably the weakest schedule BYU has faced in decades). He squandered one of the best defenses BYU has ever fielded on that gritty trainwreck of a quarterback called Riley Nelson. He has lost to Utah 4 years in a row, often in games that weren't even competitive. We haven't finished in the top 25 since Max Hall, bless his Ute-hating heart, graduated. We typically (although not in the last 3 games) scrub the floor with D-1 bottom feeders to pad our record, but struggle mightily against decent competition. And most disturbingly, we don't seem to be moving beyond this level of sustained mediocrity. Trying to say it's all injuries this year just doesn't explain the trend over the last 5 seasons.
Bronco supporters seem to have a bit of Pangloss in them: they believe this is the best of all possible worlds for BYU football. I don't agree, and I think that Bronco's first seasons proved that BYU can still field teams far better than the mediocrities we've seen since. I just don't think Bronco's teams can do this anymore.