I like malus for bad rulers, even if in the end it will result in the same effects.
As a matter of fact, it might even be easier to balance.
And it also allows for slightly stronger effects, such as:
+5% Commerce Income per Finesse above 5
-5% Commerce Income per Finesse below 5
It is easier to design, explain and understand it if you don’t have the shift in it. It is also less prone to have errors without the shift.
It is the same effect as Finesse * 1% while shifting the base commerce by five.
I say we should follow the “keep it simple” method here as we get no change in effect.