The point of the loss of personal unions to non-european people, was that vassalization would become easier for the RotW. This change was not made however, and you still can't vassalize outside of your religious group. So now royal marriages are worthless to the RotW because they are now just +25 to relations and legitimacy over time. Make vassalization outside religious group possible (maybe require you have a royal marriage with them if they are outside your religion group.)