If you would be doing this by dungeons runs, you would need 500 6* legendary artefacts for the last stage of getting the sacred shard....I doubt that you can do this with the 1560 energy you will get at max for the 500 gems.

Running campaign might be different...but you will get only 195 runs from that amount of energy at 12-3 brutal...judge by yourself whether you could achieve the necessary points for that...and don't forget you need to make some additional 12k+ points to unlock the keys..

It would cost you far more than 500 gems. The math bears out to about 18000 energy if spent on Dungeon 20 to go all that way down that path, or 141 energy refills. 

The legendary book is a much better target, IMO. 

Somehow I was thinking the same..;-)

i

The shard is more like a lotto ticket.  It has almost unlimited potential, but you could spend 10000 gems for one and still get the worst epic out there.  With the book, you may not be able to decide which skill it will enhance, but you know exactly which champ it will enhance.

Good comment.  We get lulled into the possibility instead of the reality.