FG says Flahery has a 1.7 WAR with a 96 FIP- but 0.7 RA9-WAR and 117 ERA- in 124 innings, while Mize has a 1.2 WAR and 101 FIP- with a 1.7 RA9-WAR and 86 ERA- in 105 innings. The main difference for Mize is he is getting LOB luck (80.3%, vs 71$% for Flaherty). So, if you look under the hood, Flaherty is pitching "better" than Mize. But, the results are what they are.