Core turrets are, from what I saw, as cheap as T1 turrets, and then 5 times as powerful. And then, note, that spider turrets specifically, get 5x engine damage, and hence totally invalidate the whole *We are not enableing T4 Riot starships because no enemy ships would be able to move again, ever* when Spider turrets do the same thing, easier, and can cover all planets.
Its so insanely OP its not even funny.
The rest are not much better. If you get Core turrets, you just place them on all planets, and ignore the inferiour, more expensive, and more energy intensive versions, even if you spent knowlege on them. Admittedly, if you unlock T3 of a turret, it might get you more firepower if you crowd it all on a single planet, but that is not really worth it at that point.