Even then, I can name numerous other relievers who are reliable the majority of the time.
Some teams just build bullpens using primarily cheaper high upside/no consistency pitchers. But do you think the Yankee bullpen with Chapman, Britton, Ottavino, Green, and Betances has a lot of volatile pitchers? Or the Brewers bullpen with Hader, Jeffress, Knebel, Barnes, etc? Or when the Royals had Holland, Davis, Crow and Collins?
Some teams just use good pitchers in their bullpen.
dgalehouse summed it up. Some relievers are crapshoots, but so are some starters...