I cleared the Paladins and Dragons on the second week with 7 Djinns, 32 Gargoyles, 34 Pikemen, and 21 Archers (without magic). I deliberately went to the Warlock's Castle because I "believed" I would find a portal. Although I had enough resources to reach the last floor, as I didn't waste time with other heroes. The next day – I dealt with the main Castles. And on the first day of the third week – I finished them off.

Added 3 minutes ago
The strategy with boats didn't surprise me. I've seen the summoning magic for boats, and I also built the second Castle in my time, but I didn't particularly rely on this approach. I immediately went down the path of STRENGTH – if I need to break through, I need to break through as quickly as possible and defeat everyone: cannibals, phoenixes, paladins, dragons, cyclops. And I need to level up the stats, especially the "knight" stats.

Added 1 hour 28 minutes ago

2 Zingel
Either you were very lucky, or I was very UNLUCKY. In my case, the Sorceress had 4 heroes, and 2 of them ran to opposite ends of the island.
Because of this, I lost a day, and I couldn't do anything.

To prevent the AI heroes from scattering, you need to "lure" them with empty Castles and uncollected resources. Although, in my opinion, the AI in the first part is one of the most "intelligent" in some aspects. However, it is just as predictable (especially in combat).