Tiered 5 star crystals
First of all don't really believe the pulls are random. They seem tilted to low rated champs. How about tier catalysts? Not sure about the percentages, but this is just for thought.
15000 shards- 20% featured, 30% above ave, 40% ave and 10% below ave.
10000 shards- 10% featured, 15% above ave, 60% ave and 25%below ave
5000 shards- 1% featured, 5% above ave, 30% ave and 64% below ave
The rating would be from a tier list from Seatin etc.