The reason Allomancy doesn't match Preservation is because Shardic Intents are not self directed. I don't have the WoB, but Shard Intents are applied to the Shard's outward actions, not to themselves. Preservation isn't about self-Preservation, and Ruin isn't inherently suicidal. Preservation's magic system preserves all the power of the user - it doesn't expend any of it, as happens in Feruchemy. In Feruchemy, everything comes from the user. Stuff is expended, not preserved. Allomancy has power coming from Preservation, thus preserving all the person's power.