Had Soo-Won been a little more intelligent, he would have also stationed guards by Yona's room and only Hak would've batted an eye. I really would have loved to see both Soo-Won and Yona rule the throne together (but don't get me wrong, my OTP is Hak and Yona).
Actually My Dream team goes like this - Yona be the Public figure as the sole Ruler of the kingdom helping it's people, with Soo-won as the strategist aiding in the internal court & political matters while Hak supports them in battlefield & maintains peace in the borders. Just imagining it gives me Goosebumps!! Those 3 would have made an invincible team even if there were no Dragons(don't get me wrong. I LOVE THEM!!) to help them.
Because, Princess Yona is 10 times The Ruler material than King Soo-won could ever be.