Well, if you're looking for a tidy fantasy where the king is always noble and the knights are all chivalrous, Bernard Cornwell's trilogy will give you whiplash. The genius of the thing is how leadership splinters across multiple claimants—Arthur, Mordred, the various British kings, the Saxons—and none of them ever truly holds the whole island. Power isn't a throne you sit on, it's this fluid, temporary thing that shifts with every battle, every broken oath, every whispered rumor Derfel hears in the hall.
What stuck with me most was how Cornwell frames leadership through necessity versus legitimacy. Arthur's the effective ruler, the military genius holding everything together, but he's forever hamstrung by his oath to protect the 'true' king Mordred, a useless boy. So power becomes this corrosive dance: Arthur has to constantly negotiate, manipulate, and sometimes outright defy the very legitimacy he's sworn to uphold, just to keep the Britons from collapsing. It's exhausting to read about, frankly, and you feel every bit of that weight on him.
And then there's the religious power struggle, Christians versus the old gods, with priests and druids pulling strings in the background. It all adds up to a portrait of leadership as a kind of desperate, muddy pragmatism, where the 'good' ruler isn't the one with the purest heart, but the one who can keep the wolves from the door for one more winter. Even then, you're left wondering if any of it was worth the blood spilled.