But you can request several saves from this battle, which means you'll have to get all 100 morale points during the playthrough, and that's a challenge.

What does "request" mean? I don't keep 100 saves for each battle. It's not specified in the rules. At most, you'll get a save from the beginning, middle, and end of the battle. In my opinion, three saves are enough for a battle: before the attack, which will always result in the same landscape; the beginning of the battle, to see the troop arrangement; and the save from the moment the battle is considered looped. What is a looped moment in a battle, read in the topic "Tournament Troubles." Then, when they conduct the battle, sometimes, to save space and speed up the Heroes 4 program, they overwrite the same save and load from it, etc. The fewer saves in the saves directory, the faster the load and save process. Also, look at how much the saves from Heroes 4 weigh.
Your verification method doesn't work. At most, you can request 3-4 saves from one battle, and there are dozens of battles. Will you request all the saves from all the battles?
This is not serious. But what does it matter? This battle can actually be won; what complaints can there be?

Added after 8 minutes

i.e., if ambushing is prohibited, does that make the Minotaur the strongest unit? Because you can say that he was lucky n times in a row and deflected the damage... is that right?

Well, almost. But if there are many units, he needs an open ambush. It is allowed. But if the Minotaur is attacked by several units and a couple of archer units, he needs to deflect the attack, say, 4 times in a row from one save to the next. I think such a battle is theoretically possible, but not in reality. In reality, you can still fight when the Minotaur needs to deflect a maximum of two attacks in a row from one save to the next!! But since there are no rules on this, I don't know, maybe someone will find a brazen player whose Minotaur will always deflect 3-4 attacks in a row from one save to the next throughout the battle.
On the other hand, the Fairy still remains strong against slow units. But let's not forget that the Fairy can be sped up, the enemy can be slowed down, wings can be cut off from flying units, and arrows can be lured away from archers - then it's easier with Fairies than with Minotaurs. And ambushing is not needed here, but it may be necessary to choose the right landscape.