The 3rd stage of the annual John Van Caneghem Tournament (2007).

And here, the 6-day result seems realistic to me.
RAPER is right, Fireball padded something.
Desse could have taken pathfinding, visited Utopia,
and wiped out the dragons (possibly capturing the green Castle along the way).

I didn't pad it for the fun of it. If you take pathfinding and tactics (meaning arches aren't needed), like you did, then Desse is left without Air. And without that, the Azure Dragons cannot be killed.
Personally, I am 99.99% sure that completing it in 6 days is impossible. On day 6, the level 3 guild is being built, and leveling up Coronius and delivering the spells is also a major problem. Plus, you have to protect the snipers carefully, which slows down the run. In 7 days - maybe it's possible.