The title says it all. If a region lord wants the Banker to handle those mundane issues of food and money within the region, then let them!
I know this will bring some regions/realms back to the good ol' days where the Banker ran all of the food distribution, but the region lord would have 100% control over who their Steward was, it is their region after all! The profits of food sales would still go primarily into the Lord's pocket anyway.
Just something to consider.