Yes and no.
IF we put forth a literary conceit that Gnomes are inventors, and then never show gnomes inventing anything, then our conceit is unfounded. It is telling us something that we are not shown. And one of the big things in any sort of writing is "show, don't tell". And part of this is because you can tell someone a "fact" about your story/world/character but if it doesn't come up, if it isn't shown, then it feels false.
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If the only reason for halflings being overlooked is because we say they are overlooked... then it is a weak literary element. IT creates dissonance because there is no reason for them to be overlooked, no real way to show it in the story, and they end up feeling less tied into the story and more just cartoon stickers pasted onto the world.