I think someone got confused and misread shit lord with Sith Lord. Thousands of years of shit posting will eventually cause some confusion to later generations.
I like the idea. Probably could have given more context earlier on in the story.
Spiritual warfare isn't really all that common in stories and even then they are usually pretty obvious or have more tells to them.
Edit:
And again the worst thing that can happen is the MC becoming Better...
You don't have to dive for them. There are enough of them that wash ashore. There were communities who made a living solely out of washed up kelp harvesting.
So, is the fabled Roman Concrete now a thing? The one that gets stronger over time in seawater. Or is that the Summerstone I vaguely remember reading?
Edit:
What about using nets to catch the Ironborn boats?