He didn't fall too far behind me.

Yeah, and I spent 4 days resting after taking Castle on the continent where Magnus lives. I should have immediately gone to the Dungeon, but I was still waiting for the Archons to accumulate, and as a result, I couldn't upgrade 3 Angels from the reserve. If I had gone immediately, I wouldn't have taken 4 Archons from the reserve, but I would have upgraded 3 Angels from the reserve, and there would have been only 1 fewer Archon when diving into the Dungeon (not 17, but 16).

Added 6 minutes later

But why is Dessa the main hero then? Did he kill Magnus?

It's just that the Celt with Hippogryphs was defeating Phoenixes and Archdevils because his specialty is Hippogryphs. And Dessa started leveling up when the Castle on the island was captured, and the Hippogryphs took a backseat. Dessa is also a Logistician, so he moves faster, which is why I chose him as the main hero. That's why it was more important for me to take Pandora with the Celt. Besides, Dessa already had Logistics, and I didn't want to give Diplomacy to the main hero.