What is the source of the Mages’ power?

I've never played a full game against a human player, only against the AI, so my next conclusion is for playing against the computer. In the early stages, mages are weak, but when the Oracle hero has Spellpower plus Leadership and Luck, she's a monster. She has a tactic against any army: she uses Frenzy and Enslave on some, Clone on others, and Armageddon on others... Also, you can leave a second hero to guard the castle, and the Oracle can pass on the necessary experience through Mentoring... All neutral creatures are either defeated without losses or join you.... The Oracle can carry Titans, or Titans and Rakshasa with her... I definitely defeated (the main hero) of the Dwarf, Necromancer, and even the Dark Mage this way... You only have to get creative if the enemy has immunity to Dark magic... and with Enslave, you can defeat anyone.... And of course, you need to remember about artifacts that greatly enhance creatures...