That's a lie. You simply had the Grail!!! And Agrilaal' same brain was tweaked, otherwise he wouldn't have waited for the week. And on a random map, Haven won't be OP because its first units are weak, while fairies or furies will bring far more resources and other goodies at the start of the game; there will be a huge leap in development for those two castles.

The Grail had only been standing for 4 days by that point :) I simply put all the peasants on horses. And I fought Agrilaal near the fort. He attacked me himself. I just collected all the money chests and drank it all away at a trading post. By the way, there are still some peasants left. But I didn't build any angels at all.
Archers are more than enough at the very beginning. And only them. You can turn them into crossbowmen, and with Bless they just tear everything apart. As for griffins—they are a double-edged sword. First, enemies reach them immediately because they are "fat" (high priority), and second, you can't tell where this miracle will land after Battle dive; how many times has it blocked the cavalry:)