Advantages of Mages over other races.

I don't quite understand the connection... why do mini-arts require more knowledge? ... it seemed to me that maximizing racial skill was what mattered... it's good when an artifact gives +1 to a racial skill... and the higher the hero's level, the greater the bonus from mini-arts.

The more knowledge, the higher the effect of the mini-art; racial skills allow you to create mini-arts with 1/2/3 effects, depending on how much you've upgraded them.

For mini-arts to be effective, you should get as much knowledge as possible, which results in mages having around 400 mana, while 200 mana is usually more than enough for combat. 200 extra mana remains, but instead, I'd like to increase combat stats.

As for the "native" stats, it's all a matter of luck; whether you want it or not, the random number generator decides how much knowledge you get, and there's no way to influence the probability. You should always visit the buildings that boost stats with all your heroes; everything comes in handy. And when creating mini-arts, just equip artifacts that only boost knowledge (if you have a choice in your inventory) and make them as effective as possible. At the same time, if you increase your knowledge or find a couple of extra artifacts, you can sell the mini-arts and create new ones – there will be no loss of resources in this case.