I think you may have a little mistake in your judgment. Joint structural idiom is an idiom in which the structural relationship between the first two characters and the last two characters is juxtaposed. For example, 左顾（eyes left）右盼(eyes right)That means looking around, left and right. But指鹿为马isn't, it comes from ancient Chinese allusions, a minister is very powerful (too big than the king), so he called the deer（鹿）to the horse(马) before the king and other ministers, others were forced to agree, it compares casual, wrong sharing without saw.

什么是联合结构

不是