I think “yao” shows comparisons under this circumstance, and can be seen as abbreviation for “还要/hai yao”.
eg：
-你比我想象中还要美。You are prettier than I thought.
-你做的饺子比餐馆做的还要好吃。The dumplings you made is better than those of the restaurants.
“要/yao” is quite colloquial, and normally used with “要......得多”
eg：
-去地铁站的距离要近的多。The distance to subway is much closer.
-这部电影要有趣的多。this movie is much more interesting.
