Is this race starting to become actually competitive given the shifting national environment and Cunningham’s strength?
No. This state is getting whiter and it's not D-friendly whites either. No Democrat will win this state for the next century.
We're seeing the same thing play out in SC as is around many states. A lot of the rural county democrats are moving to the GOP and the urban areas like Charleston, Columbia, etc are trending to the Democrats. Even Greenville County trended somewhat left in 2020 even though Trump still won big there.
There are five counties in South Carolina that voted for Obama twice and Trump twice - Barnwell, Colleton, Calhoun, Chester, and McCormick. And Biden generally did worse than Obama throughout the rural parts of the state, while improving in Charleston, Columbia, and Greenville as you noted above. This is just a further manifestation of the widening urban-rural divide between the two parties.