Well, if you lack knowledge and mana, I advise you to develop advanced Wizard skills – mana regeneration, unstable mana + arcane knowledge. Then you will have enough for meteor showers and other spells. The only problem remains: you are busy with the ballista and druids, but if the enemy hero goes first, for example, Sinithar, and your ballista is gone – what's the point then? Moreover, if you develop the hero in this way, it turns out to be not a Ranger, but a mage like Ashan, who combines combat machines with spells.