The most challenging maps for you.

The AI unleashed the main hero of the red faction, and he went straight to my lands.

Stop! How is that possible? Red cannot enter anyone else's territory except their own (lava): mega-garrisons prevent it! Explain or provide a save file. Maybe he learned to fly (although he couldn't - but I also had a flying enemy, only green)?

I tried to defeat the Archons and defeated them head-on without any tricks, and at the end, I had to defeat approximately the same number of Archdevils.

When the army is very large and there is a lot of mana, you can defeat the Archangels in the Pandora's Box and head-on; but it's easier to destroy the Archdevils at the end because they don't resurrect each other; at least, I defeated them without any difficulty.