Of course the Shardworld itself, given that most of them were designed by Adonalsium was important that made Investiture manifest in certain ways, as was the level of Investiture. As is the Intent, like you agreed. That was my point. That certain Intents would make certain actions impossible for the Vessel as with time they would become more and more aligned with their Shard's Intent aka the plot of Mistborn era 1. Don't misconstrue my argument. I said Endowment's Intent allowed more freedom of action.
As for Ruin, I doubt he could smite them with Preservation present, heck even with only Preservation's Investiture present. But since he had a hand in the creation of the world of Scadrial itself he could effectively smite them via natural disasters, which he did.