The game seems rigged. NEVER received a legendary even with all the yellow, purple and blue Shard i have received
game is not rigged in terms of 'not giving you what you want' - click on little "i" inside summoning portal (just to the right from mystery shard icon) and you will see your chances (same for everyone).
Lets see ...
Ancient: 0,5% chance for legendary (that translates to ON AVERAGE one leg every 200 shards)
Void: 0,4 % (1 leg from 250 shards on average)
Sacred: 6% (slightly more than 1 every 17 shards on average)
Setup is for you to either spend BIG $$$ for lottery and eventually win (30$ for single sacred ...), or do not spend at all and hope for the best.
I see no point in spending little - will give you no real benefit.
When they have players spending 1-2k$ each month no matter what, there is no reason to provide better chances...