Why was Addison Reed's stint as closer so frustrating?

The right-hander gave up hits at an alarming rate (.261 BAA, .323 BABIP against) last season on his way to a 4.75 ERA and a 1.36 WHIP. He's been unable to translate his outstanding command rate from the minors to the majors. With roughly two-thirds of his pitches resulting in strikes and his phenomenal minor league record, it seems safe to deduce that he's around the plate plenty often, so what is the problem?

As 2012 wound down, reports surfaced that Reed's velocity was dipping, and a knee-jerk reaction might be that, physically, something wasn't right. But he was throwing a lot of stressful innings (in terms of batters faced and number of pitches), so it'd be understandable that by August and September, he'd be worn down.

Judging from PitchFX data, Reed's repertoire needs refinement in order for him to have success against MLB competition. His infrequent use of his changeup (roughly one-tenth of the time) probably didn't do much to keep the opposition from catching up with some of his fastballs, which are otherwise superb weapons. Fangraphs writer Bradley Woodrum discovered that the big culprit might be Reed's easily punishable slide pieces, though. The 24-year-old lives around the zone so much that it's kind of a problem.

Reed doesn't figure to end fantasy owners' disappointment until he dictates to hitters more often. He may have a ways to go to understand that a pitch which ends up outside the strike zone has a purpose. Roto owners will have to put some faith in outside forces like Don Cooper, one of the more respected pitching coaches in baseball, if they're to invest. Reed may be elite closer material, but, as 2012 showed, he's not close to arrival. It could come quickly, but if it doesn't, the upside is tempting enough that he may warrant a bit of a reach to be a roto manager's second reliever.