John Crowley's, "The Deep" may be something you'd enjoy. It's set in a fictional world going through a feudal turnover in power akin to the war of the roses. There's some weird elements as well with the world's cosmology.

The Quest of the Holy Grail I found incredibly boring and one of the worst editions of the Arthurian legend, mostly because it was so concerned with lecturing on morality and politics in such an inconspicuous manner. It's arranged in a way where a knight of the Round Table will come upon some challenge or quandary that, if overcome, would lead them to the Holy Grail. The story is a part of the Vulgate cycle where England, the Round Table and the court of Camelot are beset with moral rot and decay, so -spoiler alert- on every occasion the knights fail in their challenge. Importantly, they don't fail because they didn't have a big enough sword or strong enough arms. After each segment, a member of the clergy or some kind of cleric appears to explain to them the various ways they have failed to live up to the chivalric ideal, sinning and insulting God, either through greed, arrogance or cruelty. God didn't allow them to overcome their challenges because they were not behaving chivalrously. It reads as a book for moral instruction by religious fanatics, chastising the knights and the reader. After each exciting play, you have this passage where you are lectured on how to live and how a knight, lord and king should treat their subjects in accordance with God's will. I didn't enjoy reading, but it's an important text historically in relation to chivalry, and it seems like it fits what you want.

If you want some historical accuracy, I'd check out Maurice Druon's Accursed kings series, which is set in 14th century France (and apparently inspired Games of Thrones) . For an Arthurian setting, check Steinbeck's Acts of King Arthur and His Noble Knights, which starts slow and is a bit out there. For added court intrigue, Alexandre Dumas' Valois series.