Well maybe. I don't want to overload the setting though. I more want to reinterpret elements than to include others.
Right now I am using a few Ideas from Roshar to come to this:
It was not the Lord Rulers fault that the planet came to close to the sun. In fact I am thinking more like some outer force like Odium or probably something more like Guile and nudged the planet toward the sun, while splintering the only Shard on Scadrial. There is and was no ruin, no preservation nor Harmony. Feruchemy and Allomancy are both stemming from the shard mhh.. Introspection? Feruchemy is about understanding oneself, using your own abilities and harness them to great extent. Allomancy occurs only due to Snapping which can be seen as a moment of self-understanding under great stress.
So anyway. Guile came and splintered Introspection. He also created Hemallurgy (stealing powers seems close enough to Guile ) and created the first Kandra and Koloss with it. His plan was to slowly let the planet drift toward the sun while the Kandra and Koloss (both immune to the heat) would sooner or later collect all the Investiture of Introspection with Hemallurgy. Guile itself left Scadrial while his agents worked. The Kandra had the order to give Spikes to humans which over time would turn them into Kolosses. Kolosses themselves were to obey the Kandra. While immune to the heat the Koloss to not fare well in the climate of the final empire. The Koloss bands only stay in the Empire for a year or two before wandering out into the deserts. Later on they might come back for another year and so on. Outside of the final empire there are Koloss bands roaming most of the planet as a lot of Guiles plan has worked.
Introspection however did almost get whole again as the Rashek held its power for a moment. Only due to the whisperings of the Kandra was he convinced to let the power go and become a Sliver. He did have the time to stabilize the Orbit of Scadrial though and make the ashfalls / other changes to ensure life in the final empire.
Since then he has been tricked to, influenced and been corrupted by the Kandra. As of now there is not much Introspection left in him, Guiles Agents however were not unchanged by the splintered Introspection. The Kandra no longer are united in their purpose to destroy Scadrial. After all they would die themselves, the like it how it is. They even made the contract with the Lord Ruler to ensure their mutual trust. The Koloss are still loyal to Guile but always relied on the Kandra to give them directives. As such they are also a unreliable factor.
So in the end the only way to fix the planet is to find a way to make Introspection whole again (in the process probably either converting the Lord Ruler back or overthrowing him) before Guile comes back and throws a fit and destroys the planet because his clever plan did not work.
Now I am looking what the splinters of Introspection could be. I don't want Introspectionspren but the Splinters should exist and do something. Not sure what though,