I think your crayfish are amazing. It is clear to me, from your observations of the HBG, that they are supporting your pond's forage substantially. It's just that they have been too much of a good thing, that's all. You'll find that goldilocks balance when you fill that gap that is missing (a predator that will seek and eat 4" crayfish). The goldilocks amount of that predator will allow enough adults to survive to replenish their standing weight. Forage production may decline in this case if you don't replace the lost production with other prolific reproducers. Crayfish are high energy forage ... even better than BG according to one reference.

My sense is that your pond never reaches its carrying capacity of crayfish and that they grow maximally. So it works like this. Way more spawn is produced than would be required to replace the adults ... but they are continually cropped never attaining the carrying capacity. Under such a scenario, the pond can produce a greater weight of crayfish in one season than the pond could carry were there no predators. So instead of stunting they continue to grow all season providing forage along the way.