the main thing is to start by recruiting Arantir, level up his Spell Power, and I also took Expert Sorcery... if you level it up correctly, he'll have 40+ magic skill when approaching Holy Flame, which eliminates the need for a Death Avatar because the Phoenix turns out to be much stronger!

Maybe I'm missing something, but why summon anyone if you can just overwhelm them with numbers, regardless of their knowledge and magic power? And even attack and defense. Just spend an extra week in one of the cities, accept caravans. How can taking a 6th city be considered a problem when you already have five developed cities? Especially a city that the hero doesn't even leave? Let him have the Tear of Ascha there – sooner or later, he'll be defeated.