A word has no power if it fails to communicate what you intend it to. (Except you intend to destroy your opponents hearing by sheer volume, in which case you can use any word)

There are countless idiots who have incredibly broad vocabularies. They are still idiots. Therefore your argument is invalid.

Actually, I don't think a word has any power if you're the only one who knows it...

Maybe if you and your buddies know a word that nobody else does, it has some power, but the only way for a word to have any use if to share the meaning. Otherwise it's no good.
If you try to insult a person with a word they don't know, at most they'll be dumbfounded, but more probably they'll just laugh at you for your ridiculous made up word.

Wow I never knew that.