Unfortunately, my friend, I think that when leveling up three branches of magic, the hero always becomes an Archmage. Maybe, if you don't fully level up the combat branch right away, you can switch to another class later, but after leveling up all three branches of magic, the character will become an Archmage because the weight of the three magic branches prevails. I also leveled up like that when I was testing, and my Barbarian became an Archmage (lol). Therefore, if you need a different class, you should only level up two branches of magic. In my opinion, the best advanced class is Field Marshal (tactics + scouting), but it's up to you to decide.