We can invoke RAW if we accept the simple fact that the words on UA actually have meaning. You do not seem willing to do this as you attacked how valid and how much work is put into the wording of UA. But without accepting the wording, it all becomes "I don't think it should be a weapon and so it isn't". The wording on the UA clearly states the horns are a weapon, which I think was done to avoid abuse with monks and tavern brawler.