Is it off topic to ask whether certain weapons common to fantasy RPGs (e.g. battleaxes with extremely large blades) would make feasible real-world weapons?
If the fantasy weapon has a grounding in real life, then I suspect it would be on topic.
So, asking if a buster sword is practical would be off topic as it is a fantasy weapon with no grounding in real life whatsoever. However, asking if a "large battle axe" could be used as a Fu would be on topic. Or even what martial art uses "large battles axes".
Weapon identification is on topic if it is a real weapon. A question speculating on the origin of a fantasy weapon might be best asked on scifi.
Some fantasy weapons do look no stranger than real life ones...
In general I think your proposed question would be a bad fit on the site because it would lead to speculation, guesswork, opinion and extended discussion - all things that are good on a forum but not on a Q&A site.
The thing to remember is that the question's subject matter is fantasy, therefore a lot of real world rules don't apply.
But in case you're wondering, the simplest way to answer your question is to consider current history - do any of the established weapons match the hypothetical battle axe with a large blade? If not then it's because it wasn't a good feasible real world weapon - it's not because the warriors of centuries gone didn't think of it.