I tried to explore the various way to end the game by cheating and going directly to the target. The Spell of mastery cannot be done easily because there is no magical cheat, so I decided to try the master quest.
The problem arrives at the end of the quest when you need to defeat the hermit. The hermit is simply undeafeatable because he dodge all attacks. I made a unit with the best equipment that would require more elementium that could be find in the whole game and all my attacks missed. I have a few screen shot but some screen shot simply failed to be taken.
The screen shot below show my army strength of 5000. Another weird thing, my opponent has an hero right on the quest location. So I need to declare war on it in order to get into the quest. I know that I am probably the only player who can see the location of the quest because I am on the quest, but I just fond it odd that my opponent can still camp the place.

This is the results of the battle. As you can see, the hermit received 0 damage. I had some screen shot of the unit stat and combat detail, but the shot were apparently not taken. Anyways, my unit had around 400 attack and defense power, while the hermit has 100 defense.

So I really do not see how it is possible to end the quest. My battles were resolved in auto-battle, if something special needs to be done, at least make sure that auto-battles consider it. My sovereign was only attacking with her bow, why did she not use magic spells. I had like 12000 mana and fireball, I don't see a reason not to use it.
I think the problem is the way the math is done behind the game. Probably the doge value exceed the attack value making rolls fail all the time.
Else, I suggest you try the spell of mastery and the diplomatic ending. You never know, maybe they cannot also be completed.