It's a generalization about generalizing. The case in point is using the current game mechanics to state that a specific race has always had an edge over the others, or that a biped spell caster able to "kill an adult dragon with it's gold shield up" and utilizing the mechanic in a situation that the mechanic doesn't have algorithms for nor was intended to be used as a comparison for as the current balance of power of an entire race instead of the individual character being what makes it unrealistic.
Realism dictates that those who have an advantage exploits it, and that those who don't have that advantage are exploited against. While a mechanic alone may justify that splintered magic is more potent than a draconic primal spell, at what point in the lore is that exploited and validated by the developers?
Yes, things change but what must not change are what we would call the "core truths" for the physical world of Istaria, or physics. If splintering magic truly produces such a huge advantage as depicted in the game mechanics, then why would a race that lives as long as or is as immersed in magic as dragons not have conceded that without any sort of reasoning in the lore? To justify that dragons are blind to it while mages throughout the lore's history seek guidance from and are generally trained by dragons before becoming noteworthy in the lore would be a bit backwards, don't you think? The common theme is that a mage is taught by dragons, then takes that teaching and twists it around- and on several occasions this brings more than just destruction to Istaria. That's why to support your hypothesis and that of Raptress and Akrion I would state there would have to be serious negative side effects or good reason for the dragons to continue to ignore them and call them "lesser," feeling the need to either guide or cull the masses of the "lesser" races before becoming a problem they can't (a term of still in the future) handle.