Against which factions is it easier for demons to fight, and against which is it more difficult?

The main damage of the ballista comes from the attack stat, not magic. Mages have plenty of magic points (it still turns out to be stronger than races where the stats are magic and defense).

Of course, they are stronger, I don't argue, but the catch is that no other machinist can compete against Hafiz (without a certain amount of luck, and even then, only magical races can). (Unless it's another mage who got machines early on).

And the demons were also "unfairly" treated by the creators. Other races can easily take a rapid-fire ballista without any problems, but Hellfire needs it. The same goes for fire arrows. And again, you can't go against Hafiz, even if you manage to get all of this. In general, on maps where there is a mentor, it is advisable to use machines against the mage at the end, because the lost levels will be gained for free.