Three more suggestions:
1) When a conquest is successful, barons not of your culture should lose their land. Too often I see wrong culture Barons lingering for the whole game because the AI doesn't think to remove them and has to incur tyranny to do it.
2) When Excalibur is found during the Restore the Old Gods event chain, it should be hereditary. I can understand Arthur's death causing it to be lost, but not the death of others. It'd be a treasured possession.
3) The Saxon Black Guard should not become the vassal of a Briton, as it has in my game. They should just be a free company once the Saxons are gone, or be disabled entirely.
Also:
1) There are no cultural reclaim cbs for Luguvallum or Old Tyne which are counties of Rheged, there should be as currently Elmet has pushed Northumbria back there and then just stopped.
2) I got appointed Druid. My King had Mastermind Theologian education, but the event which seems to change education lowered his education level, which makes little sense. I suggest you do something else with it rather than changing the targets education.