Also:
Make it so that a realm baseline tax can never go below 5% (perhaps halving the size penalties on taxes overall?), and that tax tolerance due to distance from the capital also can never go below 5%.
We need wealth shared across the board, not just in the hands of the ruler/duke/capital lords, which is yet another byproduct of such boons for the capital and debuffs on size.
Perhaps remove the ducal inefficiencies, the one that makes troops less efficient in other duchies, and which means they don't get their taxes in gold in another duchy... because those too strongly inhibit the creation of more duchies and thus the share of wealth.
