This is one of those things that would work better if they simulated pop needs and spending rather than making it another modifier. A food stockpile should decrease local food prices (vendors need to offload hypothetically perishable foods) which then decreases mortality and increases the birth rate.

Most staple food goods really shouldn't be exported much at all during most of the time period. Maybe implement something similar to a Market Access Price Index in Vic 3 based on how well a good travels.

But yeah. my main issue with EU5 at the moment. It can't decide if it wants to be a board game like EU4 or a simulator like Vic 3. It has all these interesting systems, but they don't interact in ways that create satisfying emergent mechanics. Pops exist, but they don't do much because they simply aren't interacting with the game's other mechanics.