It seems it is extremely hard to obtain the Legendary Heroes at the Ancient Shard, even I used at least 30 Ancient Shards and cannot get even one.  Only the special events for Potral last week may have a chance to get just one Legendary Hero.

Also, the section of the Yue Tree should change something nice to reward rather than just the decoration like Christmas tree only.

Look at the tool tip for ancient shards.  Your chance of getting a legendary from ancient shards is .5%.  That means a 1 in 200 chance.  Doing 30 ancient shards gave you about a 15% chance of getting a legendary.