Montero pitched just 6 innings for HOU in 2021.
Graveman did okay in 23 IP (3.60 FIP but 1.391 WHIP)
Maton did not help: 25 IP w 4.97 ERA and 1.618 WHIP & 4.08 FIP
Again, I'm not saying Robles and Davis did great, but they did okay, and you left out Rios, who pitched more than Davis and almost as much as Robles:
25 IP Robles 3.60 ERA/ 1.360 WHIP (3.37 FIP)
24 IP Rios 3.70 ERA/ 1.110 WHIP (4.90 FIP)
17 IP Davis 4.86 ERA/ 1.500 WHIP (3.95 FIP)