I agree it's not one size fits all
I think it's all about finding that balance of being an adequate amount for your livestock and finding where your export is also adequate.
I agree with this. I might be mistaken, but I have always thought of the recommendation as a blanket statement of "If you will not or cannot manage nutrient export, reduce the nutrients going in, in the first place."
With fish, and lots of other added complexities of individual setups, it might not be the best route. For me, I'm trying to increase the nutritional value of the food I add, so that I can put in only as much food as I want in volume. Like using a drone to delivery a pizza with a bunch of nutritious ingredients instead of doing a military plane drop of pallets of generic pizza hoping that everyone gets what they need from the generic ingredients.