If you’re adding more and more different shards for different mythics then the chances of any dragon shards in general over say inner fires or mystic fragments is going to increase, making it harder to get those other drops.
Dispite what PG may have intended with these Draconic chests, people are not claiming them primarily for the dragon shard drops, they want the other drops. So as these chests get flooded with more different dragon shards their value to us will be lower.
I personally have zero interest in Hueso shards so those are already a dead drop to me along with xp boosts and hammers. Even if you cut the average drops of Hueso shards down to half of what it is now, the drop averages for Winter Shards has to come from somewhere and the only place for it would be to lower the drop averages for everything else.
If you have a bag of 10 Red, Blue, Green, Yellow, Orange and Purple blocks each, even if you take out half the purple blocks and put in 15 White blocks, the chance of pulling any of the other blocks has also dropped. Then next season when you take out 10 white blocks and put in 15 black blocks the average for everything else will again decrease and this will happen every season as the chests get diluted with more festive shards
This would be taken care of if instead of Hueso and Winter Festive shards we just had generic festive shards that worked on any festive dragon. Yes it would come at the cost of not having a certain festive’s shards no longer dropping once you have enough to max them but that would still be preferable to having specific shards to a dragon you dont want and having the chests get diluted more and more each season