But no, everything seems quite simple (difficulty level - warrior).
One thing is clear - success lies with "rushers." Those who stay in their castle for too long and don't venture out are doomed to face difficulties later on.
All missions are completed successfully and interestingly, as long as you don't imagine yourself as a mayor and a successful economist. After all, this is about military action, not peaceful development side by side with friendly neighbors ;)
Regarding this mission - no one attacked, I attacked and defeated everyone myself. There were no excessively large armies (version 1.6).
I didn't get Phoenixes, I don't know if it's a bug or not, I think I didn't collect the entire set (I had a dwarven helmet, boots, shield, and armor). So, first, I killed the dragons, then I took down Cole. That's it.