A banker's access to food data isn't anymore than a Duke already has
Correction: A banker can see a composite of all the information that is available to all the dukes put together. No offense meant here, but as the banker of Pian en Luries, you have the small city of Poryatown and the medium city of Askileon to feed. Not exactly a difficult task, especially when your realm has a 150-160% food supply. In such a case I can see how the banker's job would seem to be a bit... superfluous.
However, when your realm grows a bit bigger, you will appreciate the overall view that the banker has. Try feeding a realm of 5 or 6 duchies on a food supply of just over break-even, and you will see how vitally important that banker's overview is.
What is the point of even having a banker any more right now? Unless, we create like a realm bank system where all of the "ruler's share" goes into a bank vault that a banker can distribute and use in place of the ruler or something, there is no point in having a banker. Or if lords are given the option to let the banker have control once again of their food stores directly, I don't see why we have this council position.
Come on... please have some patience. This is a huge change, and Tom has only just now implemented the first parts of it. He has already stated that the banker's position is not going away. We will find a way to fit him into the hierarchy with some meaningful tasks.
