Not a bad argument.
Bird really is a better bowler with record but just the conditions go against him.
While Maxwell averages 40 to Marshs 30 in shield cricket.
For what it's worth, isolating their Sheffield Shield bowling:
Steve O'Keefe - 54 matches, 95 innings bowled (107.72 balls per innings), 24.30 average, 60.55 strike rate, 2.40 economy rate
Jackson Bird - 34 matches, 61 innings bowled (111.84 balls per innings), 20.63 average, 42.11 strike rate, 2.94 economy rate
Glenn Maxwell - 31 matches, 47 innings bowled (56.81 balls per innings), 38.48 average, 72.16 strike rate, 3.20 economy rate
Mitch Marsh - 36 matches, 39 innings bowled (72.21 balls per innings), 27.01 average, 48.55 strike rate, 3.33 economy rate