The bullpen has been bad, but calculating a percentage of save opportunities isn't really an accurate representation, because of how it treats "save opportunities."
Take Kendall Graveman of the White Sox, for example. He shows up with 5 saves and 4 blown saves, which makes him look ineffective. It seems like only a 55.6 percent. The issue is that the four "blown saves" all came in innings prior to the ninth. Yes, they were "blown saves," because he was pitching in what would have been a save opportunity had he finished the game, but the likelihood of him actually doing so was slim, because Liam Hendricks probably would have gotten the ninth.
But because he didn't get the save when he pitches well in the eighth and Hendricks finishes, those games don't help him in that 5 of 9 calculation. Said more simply, a reliever pitching the eighth can often get a "blown save" to count against him, but isn't given the opportunity to get a save to count for him.
That's where the hold comes in. He has 14 of those. Those were times when he pitched in a "save situation," but someone else got the save (or someone else blew the game after him). In the case of Graveman, it's more helpful to say that he has had 19 "saves plus holds" in 23 "saves plus holds opportunities." That's 82.6 percent, which is a much better representation of how effective he has been.
Make sense? Again, I agree that the record would be much better with a better bullpen. My post is more about the challenge of "save opportunities" as a way of measuring bullpen success.