Aight so real quick explanation of magic in this other world.
Not a LN or WN reader, but from what I can tell, the magic system is based on REAL LIFE "theories" regarding magic, namely requiring the imagination of the spell you want to achieve.
Those chuuni chants? They help the caster imagine the spell, "Roaring fire burning etc"
Where does our MC come in? So spells take magical power to manifest/cast, BUT the MC knows the nature of fire (chemical combustion of fuel). So instead of imagining a roaring ball of fire, he's imagining the chemical process of fire, thus adding onto the actual potency by using real world reactions ontop of the spell generated effect (IMO anyways). Because instead of forcing a magical phenomenon, he's forcing a natural chemical reaction.
Imagining the water molecule H2O traveling at highspeeds is more destructive than imagining a gushing flood of water.
Imagining lightning as positive and negative ions reacting to the flow of electrons is more powerful than...well imagining a lightning strike.
He's strong not only because of his will, but because of knowledge from our world. We know how invisibility would work in practical, we just lack meaningful tech currently. The other world wouldn't able to even imagine how to be invisible without existing. We know how light works, or what it is (radiation + particles), the other world has no idea other than the concept of "light" (magical light having no heat for instance).
As an aside, this basically means that anyone who is able to mentally imagine anything, in as realistic detail as possible, qualifies for magic in our world, according to that system. If you can't "make a mental image" then you're a moogle basically.