Honestly, I think I'd add option B right away, as a passive feature.
"Every duchy that contains at least one city or stronghold increases the allowed distance from the capital before anarchists become an issue and increase the tax tolerance".
No need to build anything, just have it auto apply. It feels fundamentally wrong how the game discourages realms from having more than one duchy. And the newish size limit feels too small, there needs to be a way to increase it to what it used to be.
