I think bees are much more efficient than flies, but flies beat us. Not always by much, since I can get more fruit on one of my pawpaws by hand pollinating than the flies ever manage. But that's only in the lower part of the tree, where I can reach. My other pawpaw is always loaded with fruit and I wonder if it's self-fruitful, since the two trees are right next to each other.
By the way, whoever ordered the gingkos decided to save some money by buying unsexed seedling trees. I doubt a planner did it. It's very difficult to tell them apart until the females start fruiting, which is 20+ years later. By that time, who ever got congratulated for saving the town a few bucks on the tree order has retired. A number of places have planted only males of some other dioecious tree (I forget which one) and there was some controversy maybe ten years ago after some people said the pollen contributed to local asthma problems. The reason for planting only males is to avoid the fruit, whether it's stinky like gingkos (I think the smell is vomit) or just piles up under foot.