I guess it's cumulative specialists that really overpower them. I find that most mega yields result from specific social policies that complement with leader/civ/wonder bonuses and then having a lot of settlements with the right buildings and adjacencies. The UI remains a bit too opaque to really review this clearly.Each specialist added to the Punic Docks seems to give +2 science, +2 culture, +2 food and +1 food production.
So a total of 6 added within the first 15 turns probably means +12 science, +12 culture, +12 food and +6 production? Not sure if that's an accurate total.
Still, it's cool you tried out this experiment and while it doesn't seem incredibly overpowered, it's at least a way to get a bit of an early lead especially if you played as Carthage.