[Theory]Reason why Odium can Splinter other Shards

[The One Who Connects]

@Elenion He was weaker than the average shard would be in the same situation because he had not attained his mountain of Atium yet. All that solidified power of Ruin was still out of reach. 

@Samaldin I believe Brandon said that Preservation's power would eventually splinter itself without a holder to guide it. Odium may have perfected a technique to speed that process up. We know that whatever Odium does to splinter a Shard is very draining to him, so it wouldn't be too much of a stretch for him to try and smother the Shard like Ruin is doing, but with all his available might at once.