When you put it that way, I suppose so. However, Begus, Dorgania, and especially  Amagal had problems of their own at the time. Who sits on the throne or if they're able to hold their own in combat wouldn't matter much. No one would have the time to attack the country as a whole. (Besides, with ryen's lv at the beginning he would have been an easy target for an assassin anyway). If you play Ryen as a merciful king, sure, he's probably better than any of the other candidates, definitely better than the arrogant nobles, at any rate. Evil side though, (purely theoretical, because I don't think Trey would allow that) Ryen could be much worse than a random guy off the street. 

Imagine hearing about this as a commoner, your new king is a demon-like draconic who almost definitely harbors ill-will against humans. He is super-powerful, extremely lascivious, and spends his days hunting for maidens without so much as a backward glance at the state of the realm. He fathered countless children, many of them bastards. He sets atrocious taxes and harsh laws, making Dorgania look mellow by comparison. Worse, without Mira to soothe him, he often takes the true form of a dragon, wreaking havoc in his mindless rage everywhere on the map. Oh and his brother is trying to raise a golem army to form a dictatorship over the known world and possibly wipe out anyone he sees fit. Best case scenario, they fight each other and one of them dies with the other sufficiently weakened for the survivors to remove him. Worst case, they work together, and reduce freewill to a symbol of the long-gone past. 

Also, who will succeed the throne after him? I don't know if you're familiar with Fire&Blood, if you are, you probably understand what I'm worried about. Aegon the Unworthy is no match for him.

As mentioned before, the country is economically declining and militarily defunct. What better target of attack  is there for any of the three countries?  And what better excuse is there than a rash king with a disputable bloodline who spends his days meddling in other countries's affairs and creating diplomatic incidences?  It's sheer luck plus the support of all the faithful lords and friends around him that keeps Ryen safe and the kingdom prospering again. Lords and friends, who might not be so inclined to assist if Ryen has been a tyrant.