Sorry, I didn't mean to make it sound like monarchies win out because they occasionally get 6/6/6 rulers. Over time, the average monarch gets 10.5 monarch points per month, which outperforms a noble republic by about 300 points every 40 years and 4 year term republics by about 1200 points per 40 years. That works out to between an extra 4 techs and an idea at base cost and 18 techs and an idea at base cost. Again, that's assuming your rulers are merely average.
So, the Dutch republic getting rulers that are effectively monarchs is actually a good thing in terms of monarch points.