The Hero's Path

Was it really too easy, or is the difficulty level quite adequate? Perhaps the cost should be increased further, and the bonus for those overpowered forest archers and furies reduced? (I myself used them a lot; I only took other units for variety, alternating between them).

No, the difficulty is adequate; I had to replay many battles several times. I don't think the bonus should be reduced; I believe that the lack of soldiers in the barracks, even more than the lack of money, encourages you to try to complete as many battles as possible without losses.

Angels could have become available for recruitment, but for that, you had to diligently help Archhild (in the quests where you had to choose one of the cities).

I sacrificed a lot for them, and I sold all my mines to them, and I completed all the mayor's quests. So, does that mean I also have to build a guild there? In any case, they are useless at this late stage, plus there are usually not many warriors available when the shop opens.