As I already said, we even completed the Cultist campaign with a hero without magic, so it's all possible. It doesn't really matter how you develop Isabel. Godric is powerful in himself and doesn't require much leveling up. Without machines, Agrael will have difficulties in conquering, and without magic on the islands, the other skills don't play such an important role. Markel, Railagh, and Zephyr are magical heroes, and hardcore players complete their campaigns without magic. And Fedya is the most versatile hero because he is a good warrior, and all warrior perks work well for him, and any magic is also convenient for him; you can do a lot of things even with summons and phantoms.