Grow time. Faster crops have lower multipliers.
Not a simple adjustment to average out the same over long periods of time. If I look at 120 hours, the time of all 3 crops multiplied together, and apply each multiplier to the number of harvests I get 10.52 for Carrots, 12.41 for Raspberries, and 7.944 for Potatoes. Making the Raspberries over 50% better then the Potatoes based on the multiplier alone. Edit: the potatoes has rare drop genes so it is doing better but only because the right gene was offered.