The Hero's Path

1) I don't know about others, but breaking through to the elven city was the most difficult part. After that, there were furies (all the strong ones were killed, but they are slow and their level was raised significantly - on a higher difficulty, the hero has thick armies), the Crystal of Secrets (archer blocking), light, darkness - in short, it wasn't fast, but the path to victory was clear. IMHO, strengthening the armies won't have much of an effect - it will just take a little longer.
2) And what if we add such plot twists - quest (and not only) battles, where you don't have a carefully developed hero and a selected army, but a script-defined one? The idea was taken from the sixth installment of Might and Magic: Heroes - the battle between Azkaal and Zana.