WARNING: Minor spoilers for Wind and Truth
We know Adonalsium was able to act due to the existence of worlds and races that predate the Shattering (such as Yolen, Hoid's home world). Thanks to new information in Wind and Truth we also learn that Adonalsium fought back against the 17, although at the end he gave up in order to prevent the destruction a clash of godly powers would cause, allowing himself to die. This means Adonalsium was both sentient and at least in some capacity a "good" God. As far as Intent goes, the reason the Shards struggle to act is because they're incomplete. Adonalsium, was the whole and had multiple aspects and emotions (odium, ruin, honor, devotion, etc). Odium alone only knows how to hate. Ruin only knows to destroy. Honor alone only knows how to make and keep oaths without any nuance or gray areas. When you have something like Adonalsium, you have a whole capable of nuance; everything eventually needs to come to an end (Ruin), but there's more than wanton destruction and things also need to be grown and nurtured(Cultivation). Some things such as evil or injustice should be hated (Odium) but it needs to come from a place of love (Devotion) to truly care about the people who suffer. Essentially, Adonalsium is nuance, something the Shards lack as they're isolated and stunted parts of a whole. Rather than being unable to take any action, Adonalsium and the combined shards should be able to function normally with nuance and recognition that the world is not black and white.