Earlier quoted context omitted.
Look at it this way: if the percentage income spent on food dropped from 60% to, say 20%, that would effectively double their remaining income! I don't see how that could not affect a local economy, regardless of the absolute scale.
I think the point is that actually doubling income is a better way to increase income than trying to optimize the price of one product. What we do know is that food is already very cheap in Africa. It's not obvious that food could get much cheaper, let alone the 300% price reduction that you give in your example. On the other hand, we do know there are huge gains to be had when it comes to increasing income and econo…
This is literally creating local jobs. A job equals more income than no job. So this is raising incomes. In addition, there's less capital leaving the country buying foreign produce. So the money that would be spent anyway creates a local job, and in return is again spent locally by a Ghanaian farmer, instead of spent in Europe by a Dutch farmer. This is literally a win all around. An economy is a system, you can't just one day create amazing jobs without an entire support system around them.