Which magic schools should I choose for the late game? Or should I go for a specific artifact?

Hmm... Reactive Rakshasa. Sounds amusing. But applying three enchantments to them is a rather questionable decision. Especially in a game against attackers like Orcs and Demons. By the time they become reactive, believe me, the Rakshasas might not even survive (or survive in very small numbers). And the Mage faction's troops are poorly protected (even if you load them up with mini-artifacts, you still won't be able to match the attack power of Demons and Orcs, and even reaching the Warlock level is unlikely), and as a result, they die quickly. Besides, discussing upgrades from level 27 and above is not interesting, because you can upgrade everything you want, and any race's hero will become a real superman. I'm not even talking about the fact that such a level is unlikely in a real game. It's better to focus on the minimum, for example, which skills and abilities will bring the most benefit in a game against a particular race at levels 15-20? This is where real debates and discussions can arise, because everything is ambiguous, there are many choices, and you can only upgrade a limited number of things.