Note that @zamundaaa has previously proposed an MR (not merged at this time) for automatic brightness adjustment directly inside KWin, as opposed to powerdevil which would ask KWin (on Wayland) to change brightness.
I don't have a good sense of what the advantages and drawbacks of both these approaches are. But it would be worth figuring out which one is best for Plasma, and focus on that one / close the other one.