Warband had the same issue, the buildings in that game were just laughable. It took you about 100 days to build a farm, giving you a whopping 5% prosperity bonus. Wow!!! A school took 200 days, costing some 30000 denars, and gave you +1 relations monthly. Wow!!! They follow the paradox game design philosophy of miniscule, imperceptible bonuses that take an entire game to build up, and are static so you can't influence that 5% in any way.
Buildings and policies should unlock new gameplay mechanics, not just lazy ass percentage bonuses that are basically glorified difficulty sliders. There should be a world of difference between playing as a khuzait lord and an imperial lord because of the policies.