Secondary skills in Heroes 3.

I don't understand this phrase. Will a mage with 50 strength defeat up to 100 raiders?
And what does defense have to do with it? What kind of skill is that?

Let me explain: Defense affects the amount of damage that will be dealt to a unit. I saw a map where a Barbarian with stats (50 50 0 0)
and combat skills fought against a mage (0 0 50 50) with magical skills (they didn't have any artifacts). Their armies were equal to 6 city growth levels. In the battle, when the mage cast an expert explosion on the raiders, very few of them were destroyed (I don't remember exactly, but not more than 40). And this is a level 2 unit. This is such an awesome mage with his spells....

I completely agree with Arandor and use the same tactics... Only I have a hero in each Castle. So far, this tactic hasn't failed me. Before, I also built many heroes out of inexperience and divided the army, but now, with experience, I have come to understand that there should be one main hero and a bunch of others who collect resources, etc., in general, they save the main hero's turns and scout the map...=))))