Xaart, map “This is Legion 2.0” - from the series of strategic maps by the author under the nickname maygwan. In this series, the player has the opportunity to thoroughly upgrade the main hero and, if desired, clear many zones with monsters and treasures. I downloaded many maps by maygwan, but I have only completed 4 so far. I liked "A Dragon Adventure" and "Undead Apocalypse". Also, "Raising a Legion" is quite good (for lovers of necromancy and demonology), but with one caveat (it would be much better to get the Town Portal spell before the battle with one of the mandatory enemies; otherwise, one of the heroes will have a hard time).
Almost all of his maps are also posted on the maps4heroes.com website, in particular, here is the page “This is Legion 2.0” If you have any questions about this author's map or others, you can ask him directly there, but only in English. He will receive notifications, but how soon he will answer is unknown.
I haven't even finished reading your post yet, but I will definitely read it. If you provide a save file, we can take a look and maybe offer some suggestions. Ah, I see, I'm downloading it now...
In the evening, I started playing "Raising a Legion". I'm still in the process of completing it, but I agree that the Town Portal spell would be very helpful for Boneface! The hero cannot learn it from another. At the beginning of the game, Fireface immediately receives books of water and earth magic, plus a vial of life, so he is fine with the Town Portal. But I want to warn other players - to pass into his own Inferno Castle, the guardian asks to give him all 3 artifacts. Do not give them under any circumstances! Just teleport to the Castle. Both books are invaluable; as the game progresses, we get another book of water and fire magic, and maybe we will even find a book of air magic.