A successful siege already provides you with a range of rewards (loot, experience, influence, renown, a bonus to the settlement selection, etc.). None of which resolve all financial woes by themselves. Pillaging is simply an additional choice to exchange penalties for a boost - and introduce a trait based AI dynamic to the world that will, ideally, help with things like snowballing and developmental stagnation (previously all towns would permanently max out their projects at some point).tldr: 14k for sacking a town is peanuts. just like owning a town in the first place in bannerlord.
As noted earlier, this may well see further balancing, but I personally doubt that you will see the numbers you indicated. They would likely break the game.
@Bannerman Man From what I can tell, it should indeed be the settlement culture. Added it to the ticket.