I mean...every setting has rules. In a hard magic fantasy setting the rules of magic are the laws of physics. In the real world, the rules of nature are the laws of physics. Taking advantage of those laws is what technology is.
This is (probably unintentionally) a strawman of the rational fiction position. [Sidebar: 'Rationalist' was a horrifically bad choice of branding and 'rational fiction' wasn't a great choice either.] Nikola Tesla didn't need to know every detail of real-world physics in order to create the induction motor, and Tavi didn't need to know every detail of the Codex Alera magic system in order to scale up a telescope spell into a light-gathering-death-ray spell.
I'm basing my definition of what "Rationalist Fiction" is from
this post, specifically the "winning entry". Hence why I use words like "munchkinry" and "exploit", since those are the actual words used.
As mentioned, I have no problems with the author knowing the rules of the setting, but in RL, we know the laws of physics
imperfectly, and there's plenty of fuzzy areas even in the bits we do know. So it strikes me as unrealistic that the characters can know and understand the rules of their own setting so well, which either means they are once-in-a-lifetime geniuses, or these rules are
so simplistic that
anyone could theoretically have come up with those creative ideas to exploit the rules, and the characters just happened to be the first to do so.
So when Tavi creates a light-gathering death ray spell (akin to Archimedes's apocryphal Mirror), it's not that he's managed to figure out how to do it. It's that
everyone else reacts in surprise and astonishment, instead of immediately recognizing the principles of optics, and coming up with (or at least hypothetically thinking about) a counter. Tavi didn't need to know everything about the Aleran magic system, but the non-Tavi characters seem curiously ignorant about it in comparison.
I'm slightly more lenient with regards to exploiting
social rules, since that's basically what charismatic people do in RL, but that's only because we also all understand that social rules don't actually have the force of natural laws behind them, and are enforced only as far as people can enforce them. (Compare to, say, the speed of light in a vacuum.)