I didn't say it didn't have power. Or that you couldn't do mean things with it. Or that you couldn't be tricky and use it to earn lots of gold. (At least if you're lucky enough to have surplus food.)
I said it sucks. And I meant exactly that.
It is the last respected council position. It arguably has the biggest responsibility. People rarely appreciate the work you do. If you try any of those tricky things like starving out a margrave of a big region, you're likely to get protested out, unless the margrave is a dick. And even if you have some support in it, which is extremely rare, all it takes is one or two lords supporting him to foil your plan.
And on top of all that, if you're banker in a realm that is chronically low on food, you're in a never ending struggle to find food. And it goes on forever, with no end in sight.
It sucks.
