CR10 is barely a speedbump for an adult dragon, much less an ancient wyrm. Whether that's fitting or not depends on how you imagine a dwarven king, I guess. When I hear "King of the Dwarves", I think of a legendary figure like "The Dwarf King" of 13th Age who is a literal icon. I very much assume that dragons would flee from him, not the other way around. Obviously another person's imagination may vary on this topic, which is fine, but to me "warrior commander" feels more like a captain of the guard, not legendary monarch-champion. If the guard is a superhero, how high do the stats have to be for my vision of the Dwarf King? Does he need a STR of 30? If he does, is this game still on the rails, or are we playing Calvinball?