What determines whether I'll get a level 30 Agrael or not? And it's also unclear how to get the Crown of Leadership; all that's left on the map are 900 Phoenixes, and I can't defeat them without losses. I really liked the map and would like to finish it.

Agrael should be given at the level of Raileigh (minus N from the difficulty) - most likely, you just didn't notice (it's a bug).
The Crown of Leadership is in the dungeon - behind the blue guardian (the key is given by Lelliana, after the fanatics, I think).
Almost all battles without losses - respect! Although after 11 battles +330 charisma - the game becomes much easier.
900 Phoenixes - where did they multiply so much? (it's clearly an exaggeration).
I watched the replay - I would never have guessed to fight almost an entire legion of broodlings!
It's clear about the Phoenixes - they've prolonged the game too much - you definitely won't be able to kill Arniele.