Like I said in my first post, Jagon is much more powerful in the English version I'm playing. He did 80-100 damage with his bow (I was level 10). So spamming magic missile is useless since you'll be long dead before you take away much of his health. Same goes for Amdusias.
At high levels, a level 10 fireball/firewall (combined with level 10 destruction) kills entire groups of enemies in one go so magic missile is completely useless at that point.
Well you are right
I will take fireball only if I find something that give + to fireball
for now my creature is my shield
he die for me so I can spamm missiles