all of this is for a specific taste... in my opinion, a warrior shouldn't have a single magic skill

One is absolutely necessary; things like curse, slow, misfortune, berserk, and blindness exist—you can't fight with your army while such spells are active.......As for the mage, here is what I'll say: magic is certainly good, but if the hero is a mage, when leveling him up I usually take
1. Earth Magic
2. Air Magic
3. Wisdom
4. Intelligence (of course, if I'm not playing as Dungeon)
5. Sorcery
6. Water Magic
7. Fire Magic.
And there is only 1 slot left for diplomacy!!!!!!!!!!!!!!!! And you only use magic once per Round, and imagine that against you is Crag Hack with 40 attack and 18% additional damage; you cast something like Explosion or Chain Lightning, and he puts haste on all his units !!!!!!!!!!!! (and behemoths remove 80% of defense too.).