Why was he able to do those thing? Because he is rich from his other positions and can send gold to people like anyone else, although I do agree the banker has a decent amount of power to fulfill his job.
Wrong. Hrok got his positions - and gold -
after he stepped up to become Banker. His position as Banker has allowed him to claim insane things as under his jurisdiction -- everything from trade to dereliction of a lord's responsibilities have come under his domain of power at various times.
You requested money for your unit? Hrok knows your income. Hrok knows you've you been wasting your gold; no money for you.
Failed to make even a token effort at feeding your own region? Planning rebellion against the crown? Hrok has shot them down.
In fact, unless I'm mistaken (please correct me if I am, Delvin/whoever), Hrok has been - through his position as Banker - directly involved in every single Lurian exile for the last two years. The trick is to realize that, like in the real world, you can distill any situation down to one single element: money.
And it's the Banker's job to control the money.
