How so? You have Slaves with a cost of maybe 2 for a good portion of the game. Until the Triangle Trade comes along and increases it by 50% to 3. Then later on the abolitionists cause the price drop, maybe also by 50%, and slaves go back to costing 2 ducats.
And actually that's a nerf to African nations that have slaves. Currently in 1444 the price of slaves starts at around 2.5 ducats. By 1700 the price of slaves is usually around 8 ducats.
We can say if it work this way, we have seen only a screenshot and a conceptual description, we need to try it before.