Discussion of mapmaking works!

I finally finished the campaign about Optima. Whew, the beginning is very difficult. I spent a whole month just developing the hero. But after capturing the northeastern castle, everything becomes easy. The hero becomes strong and capable of independently defeating many neutral creatures. In short, everything is easy from that point on. I have three questions about the scenario: 1) Why is the level limited to 20? If there are no other visible limitations... 2) When I was freeing the Crusaders in the north, west of the shooting range, I was told that this was the first step and that I now need to capture castles, although I had already taken two "castles"... obviously, it's a script, but the question is, how can I defeat 40 Spectres and almost 40 Imps with a handful of archers, a weak hero, and 2 Crusaders? Is this even possible? 3) I was not allowed to enter the city of Angels through the quest gates, although I had an Angel in my army, taken from the pyramid, even two Angels (the quest says that there must be Angels in the army). What did I do wrong? (P.S. I took the Angels first, and only then came to the gates.) It's a pity that the final hero is VERY weak. Without an army and with parameters that are the same as mine, or even less, considering that I had 2 Angels, 8 Champions, and 30 Crusaders. But the difficult beginning is a big "+"