The current king also feels quite indecisive and spineless, the queen seems to be the one who is actually keeping the country from falling apart. Lunaria was meant for the same role, but Dale's foolishness was just off the charts.
To be fair, this whole act is about to bury his son's not only political but entire social life.
There is still the possibility that he's a decent king when family is not involved.
Then again, he's the king of a country where most of the power lies in the four dukes/duchesses, and what little authority he still has is steadily being undermined by the church.
He never had much real power, and I agree that there is a good chance that his marriage was the same arrangement that was originally made with Lunaria, with a wife from a family with real power to stabilize the authority of the throne. So even what power he seemed to have was actually the result of political alliances rather than a strong royalty line.