I have prepared this chart for the RAID players to see what are the chances of getting Ancient Shards, Void Shards and Sacred Shards.
On the most left is the chance to find Ancient Shards from any Dungeons or Potion Keeps and all the rest are the various Clan Boss chests.
The "Holy Grail" for RAID players is to consistently / daily achieve the Transcendent Chest in the Ultra-Nightmare Clan Boss, but it is already also excellent to achieve the Ultimate Chest in the Nightmare Clan Boss.
Thanks to Bobo for the data.