A simple fix for the absolutely outrageous wealth that guilds can generate
is to change the formula for calculating the income from a trade route.
Instead of averaging the province levels at each end of the route, average
the level of the guild holdings on each end of the trade route.

So, if I have a G(2) in Caercas (5) and a G(1) in Abbatuor (2), the income
from my trade route is 2 + 1 / 2 = 1.5 rounded to 2GB rather than 5 + 2 / 2
= 3.5 rounded to 4GB.

To be even sterner, round numbers down instead of up. And keep in mind that
any regent worth his salt will claim around 50% of income from trade routes
running through his territory, so the guild makes at best 1GB under this
formula.

What does everyone think?

Jonathan