Theo: "Don't use magic."
MC: /Immediately uses magic/
How is it "absurd" that his magic increased by 1 1/2 times? That's quite an increase. He can see his other stats, as well as that of other people, and is already aware that he has more magic than most.
With levelling not only increasing one's abilities, but there being a sudden transition when you level-up, and immediately after you kill a monster, it would be rather odd if the MC was the only one in the world to understand the concept.