To be fair, when the two allied, van Durce no longer wanted that.
Ok, but he only chose to do this after the Emperor (Largoth) decided to leave the Golden Guard on the continent.
Basically van Durce was like "We are ok letting a boat sink, as long we are not in it of course."
It's less of him being an asshole father, it is him being a traditionalistic high king.
I get where you come from, though.
An unreasonable and stubborn king that refuses to listen to advices from his own daughter, one which he treats harshly. People in the medieval times got killed for far less.
I can already give a prediction. Zyainor will inevitably come to deal with the Dwarves, his daughter will plead him to bend the knee, but Zarin obviously will refuse and say something like "I would rather see my entire kingdom be destroyed than watch it being submitted to Gardon" and then the daughter and her supporters decide to kill him, not wanting to see their brethren suffer simply because Zarin was too stubborn to listen to reason.
I mean, more open to new ideas, yeah, but standing up to Zyainor seems like an impossible task for the other mortal realms, doesn't it?
At least is better than just staying in the caves, watching Zyainor taking over everything. Because guess what Zarin, once Gardon is done conquering the rest of the Kingdoms, what exactly stops him from deciding to deal with the Dwarves? Nothing!
Gardon will have the numbers, technology, magic, support and dragons to mop the floor with the Dwarves.
Even worse, Gardon might even ask the Dominion for help, because I am sure Amari and the orcs would gladly like to settle the score with the Dwarves after they killed Rangul.